Talk:Redshift

Old talk:

• from Red Shift, up to April, 2004,
• up to August 2005
• up to Novemeber 2005
• up to December 2005

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POV pushing section removed

===Frequency-dependent redshifts===

There are also a number of causes of frequency-dependent redshift of spectral lines. This use of the term 'redshift' is in less common usage, and will not be discussed further in this article. They include Brillouin scattering [1] , Compton scattering [2], Raman scattering [3] Wolf effect [4], and other theories such as tired light theories [5] These redshift mechanisms are sometimes called non-Doppler redshifts [6], non-Cosmological redshifts [7], or intrinsic redshifts [8].

This section was removed as the statements made about the citations are not verified. --ScienceApologist 02:30, 3 December 2005 (UTC)

RfC: Request for Comments

Wikipedia Request_for_comments page

Myself, user:iantresman is having a content dispute with user:ScienceApologist (previously User: Joshuaschroeder [9]) over whether to mention that some scientists use the term 'redshift' in a wider context than is used by that in astronomy to mean just Doppler, Cosmological or Gravitational redshift. I do not contest that the astonomical use of the term dominates. Details of the dispute may be read above, and on previous archive pages.

I propose that the article includes something to the effect that (a) a 'redshift' means 'a shift in frequency' (ie regardless of the cause, such as in 'the spectral line is redshifted') (b) under the section "Causes of redshift": Some scientists recognsied a number of causes of frequency-dependent redshift of spectral lines. This use of the term 'redshift' is in less common usage, and will not be discussed further in this article. They include Brillouin scattering [10] , Compton scattering [11], Raman scattering [12] Wolf effect [13], Neutrino redshift [14], and other theories such as tired light theories [15] These redshift mechanisms are sometimes called non-Doppler redshifts [16], non-Cosmological redshifts [17], or intrinsic redshifts [18].

Evidence in support of the proposal (user:iantresman)

1. Over 500 peer-reviewed references (see list above) using the term 'redshift' in a non-Doppler-like manner.

You will note, please, that this "list" is not researched to support Ian's claim. It is only a list for keywords that he thinks supports his claim. Ian, however, has read not even 1% of the articles listed. This is not a form of evidence, rather it is the worst form of quote mine. --ScienceApologist 14:22, 3 December 2005 (UTC)

1. 5 votes out of 5 in the Discussion on the Bad Astronomy Universe Today Forum in the thread "Spectral line redshift versus Doppler redshift", including supporting comments from Jet Propulsion Laboratory physicist Tim Thompson

Off-site polls should have no bearing on this community. Moreover, you will notice that the article phrases the question differently than the question here. It is asking if there should be two articles, one on redshift being associated with shifting frequencies and one on redshift mechanisms. Most people agreed that we should not have two articles and I agree too. What Ian conveniently left out was the question of whether scattering processes etc. as he outlines above should be included in the article. Tim Thompson, I would suspect, would not be pleased to see his name used here in support of the psuedoscientific POV-pushing of Ian. --ScienceApologist 14:22, 3 December 2005 (UTC)

1. Confirmation from three professors of physics that they use the term 'redshift' in a non-Doppler-like manner, including Prof. Daniel F.V. James [19], Prof. Emil Wolf [20] [21], and Prof. Theoretical Physics, Indian Statistical Institute, Sisir Roy [22]

Red herring point. the question is whether they are using redshift as the standard definition applies or as a placeholder for another form. --ScienceApologist 14:22, 3 December 2005 (UTC)

1. Contributing editors (a) User:Serjeant who writes regarding the Wolf effect "it certainly rates a mention" (b) Prof. Daniel F.V. James (mentioned above) who writes "The term "redshift" is not used just by astronomers. it refers to any process which increases the wavelength of light" (c) user:naasking who writes "the general "Redshift" phenomenon should in fact discuss all redshift (ie. all mechanisms of redshift,.." (d) User:Joke137 who also supported mentioning non-Doppler-like redshifts.

These editors both could not answer the basic points I outlined above as to why it does not belong on the page.

As one of the contributing authors in question, I should point out that I later had no objection to removing the Wolf Effect given that the Compton Effect and other frequency-dependent effects also had no place. However I am dismayed by the level of personal recrimination on both sides over what should be a simple parenthetical remark in the article.--Serjeant 16:45, 5 December 2005 (UTC)

1. The Wikipedia Neutral Point of View page requires articles to be "representing all majority and significant-minority views fairly and without bias."

The minority is represented very fairly in its own section of the article.

Evidence opposing the proposal (user:ScienceApologist)

User:Iantresman, very incompetent in this regard, has insisted that there is a different definition for redshift than that which is provided in the article itself. In particular, he apparently disagrees with the defintion of redshift as a proportional increase in the wavelegnth of an electromagnetic wave. This is a definition that can be found in any introductory physics or astronomy text dealing with the subject of redshift. Ian has not been able to find a resource that defines redshift in any other way. Indeed, there is an indication that Ian doesn't even understand this definitional constraint (see the archive). Instead, his advocacy extends to making lists of papers that use the term redshift but do not define it and ambiguously refer to effects which apparently do not conform with the definition we outline in the article. This is an unacceptable form of research. Redshift is rigorously defined by those who refer to the term directly in the resources on the page as a proportional increase in wavelength. It is not simply a "shift" of the wavelength of light to the red. Whether they realize it or not, scientists that use this term are appealing to such a distinction.

I see an argument for perhaps including on disambig the point that some people may refer to "redshift" when they mean just a shift in frequency to the red. This is not something that should be included in the body of the article as it is so rarely a mistake as to be almost impossible to find. User:Joke137 above may have found some articles that do this. It's not exactly clear. A sentence of clarification along the lines of "Some may have used the term redshift to a shift in a feature toward a longer wavelength that does not conform to the definition found on this page, but such usage is very rare." Indeed, it seems that the reference refering to the Stark effect may be due to a mistranslation!

What Ian fails to mention is the reason he wants to include the alternative mechanisms is because he has a chip on his shoulder against mainstream physical cosmology. In particular, he wants to see recognition of such problematic ideas as tired light and scattering processes as a mechanism for redshift. Perhaps including a section in this article about such processes and why they do not account for redshifts would be in order. There is currently a section in the article that outlines the points made by those who are involved in nonstandard cosmology. In particular, there are points about tired light and scattering processes. But a sentence/section as Ian sees it would be completely inappropriate and is giving undue weight to a minority pseudoscientific position that does not belong on the mainpage.

--ScienceApologist 14:22, 3 December 2005 (UTC)

Please Support or Oppose, together with a comment, and sign and date by either adding "--~~~~" (if you have an account), or your name and date if you don't.

Nominations

Support As proposed above, --Iantresman 12:20, 3 December 2005 (UTC)

Oppose Weak support a disambig, but not of the character of Ian's paragraph. We should do it up front. --ScienceApologist 14:22, 3 December 2005 (UTC)

'Support' I agree with Dragon: don't try to make artificially narrow descriptions but instead distinguish between different uses. Also the featured Italian doesn't narrow the definition too much in the intro(Babelfish): "The movement towards the red one (also called with the English term redshift) is the phenomenon for which the frequency of the light, when observed in sure circumstances, it is lower of the frequency that it had when it has been emitted." (note the absence of the artificial "proportional increase") Harald88 22:32, 3 December 2005 (UTC)

Why do you say such is artifical? Do you know of alternative uses? I would like to see them. See below. We've found the alternative. Now it's time to disambig. --ScienceApologist 02:22, 4 December 2005 (UTC)

Like everything touched by Joshua Schroeder, who changed his user name after his suspension, this article is a mess. It is flatly wrong to say that all non-Doppler mechanism for producing redshifts are frequency-dependent. The Wolf effect is just one that is frequency independent. CREIL is another.There are dozens of peer-reviewed articles about these and other plasma-based effects. As per usual grad student Joshua pretends to know things about subject that he has no knowledge of. A change in definition is not going to fix this article. But personally I have no interest in wasting more hours arguing with Joshua.Elerner 15:56, 3 December 2005 (UTC)

The Wolf Effect and Raman scattering both are dependent on the material through which the light is scattered. Basic electrodynamics tells us that there is no such thing as an index of refraction that is completely independent of frequency. This is another way of saying that all scattering processes are frequency dependent, though they may vary in degree. --ScienceApologist 02:55, 4 December 2005 (UTC)

Support - the definition of the observed redshift should not be controversial. The various mechanisms proposed to explain redshifts range from the standard explanations adopted by most astronomers to more controversial explanations that have little support among astronomers but are nonetheless published in the literature. I'd suggest that there should be a section for redshift in mainstream cosmology and a section for alternative proposed redshift mechanisms where mechanisms published in peer reviewed journals should be mentioned. Actually, I believe that was the way the article was structured, but all mention of those alternatives was expunged by Joshua. --DavidRussell 00:58, 4 December 2005 (UTC)

I'll grant you that Halton Arp said that redshifts have an intrinsic component, but does this criticism warrant an entire paragraph in the article? I removed the paragraph for the time-being as I'm not convinced that the current wording of the nonstandard section doesn't cover this issue (people can read more about it on the Halton Arp page). I guess the question should be, why should Halton Arp's criticisms be included beyond the point that there are people that criticize standard explanations of redshifts. Does Arp hold a special place amongst those that criticize? --ScienceApologist 02:19, 4 December 2005 (UTC)

Oppose. Just say that "Other physical processes affect the frequency of light, but do not in general give the same shift at all frequencies. Such processes include Compton Scattering, the Wolf Effect, ... These shifts are sometimes referred to as redshift or blueshift, although this may be considered incorrect by some as the shifts do not in general follow the equation above at all frequencies." Include links to Compton, Wolf etc and have done with it. Incidentally, the page has been updated with good figures but a poor text edit which removed much of the clarity and rigour.--Serjeant 16:45, 5 December 2005 (UTC)

Isn't that the point, that some scientists do not define redshift by the "full-spectrum" equation, and to suggest that this definition is the only accepted definition is incorrect? Surely that does not suggest that they are using the term redshift incorrectly, only that they are using the term differently? Even Joshua now recognises that chemists use the term 'redshift' in a different manner, and likewise for Compton & Brillouin scattering, and the Wolf Effect. --Iantresman 17:22, 5 December 2005 (UTC)

Hence "considered incorrect by some". Calling a Compton-scattered or Raman-scattered photon "redshifted" sounds clearly wrong to me, but other disciplines may be accustomed to using the word differently; QED. But this is issue much less important than deleterious recent edits.--Serjeant 18:26, 5 December 2005 (UTC)

Support. This dispute should be resolved by completely separating the conceptual definition from the mathematical definition. Redshift is used in both ways, so both should be included in the introduction. The mathematical definition is more rigorous. That doesn't make the conceptual definition bad or wrong. I would remove the word proportional from the definition of redshift as a word. This proportionality applies to the mathematical definition but not the conceptual one. Phenomena are important as observables without explanations attached and without equations or any quantitation attached. The beauty of the math, the explanations, the details, and the physics is that it makes sense of the concept and limits the concept in certain situations, adding rigor. That is why this information should not be part of the definition of the word. The proportionality of the shift is a separate observable from the observable of the shifting itself. I would also include the mathematical definition (first equation) in the introduction. Turning to peer-review journals won't help us with this dispute. Imagining what would be useful to someone who doesn't know the term and wants to learn about it for the first time will help us, and that takes the modesty to imagine ourselves lacking information instead of the pride of being familiar with so many details. Flying Jazz 19:45, 6 December 2005 (UTC)

After actually editing the article to make it look how I think it should look, I guess I've changed my vote to Partial Support. I support Ian's part (a) because people actually use and publish the word in this way. I oppose Ian's part (b) because a list of all the scattering mechanisms and effects and such is cumbersome and who is to say what "counts" and what doesn't? Let's say some sneaky postdoc sets up a machine in between my light source and my receiver. His machine emits red light when it receives yellow light. Now I would argue that I am observing a bona-fide redshift due to the sneaky-postdoc-effect because I agree with Ian's part (a), but if he starts listing causes of these redshifts then why won't the sneaky-postdoc-effect be included? Flying Jazz 06:34, 7 December 2005 (UTC)

500 peer-reviewed articles indicates what "counts" and what doesn't. And even if a sneaky post-doc contrives an experiment, he can still show a redshifted spectral line, and we know what he means, even if the cause is not confirmed. But we have to give peer-reviewed sources the benefit of the doubt. That's the way the "scientific method" is supposed to work --Iantresman 08:28, 7 December 2005 (UTC)

No, that's the way the politics of modern science work. Please do not conflate the two; it is depressing to imagine them being equal. :) —HorsePunchKid→龜 2005-12-07 08:34:17Z

I think you are missing my point. You are right that the term and the math are used for individual spectral lines without applying to the entire EM spectrum. That should be in this article. But your desire to take these 500 peer-reviewed articles that refer to subsets of the spectrum and separate out how some use the phrase or the math for this observed phenomenon and others use the phrase or the math for that theoretical possibility is misguided. And I wish I could agree with you because the guy on the other side of this issue has being unpleasant. A very limited number of phenomena (three as opposed to a long list) can explain the redshift that occurs throughout the EM spectrum (as opposed to one spectral line) and are refered to by many more than 500 articles. That's a good reason for nearly the entire article to be devoted to those three phenomena and the others to be mentioned collectively but not listed. I strongly support your (a) but strongly oppose your (b). Flying Jazz 12:00, 7 December 2005 (UTC)

I'm note sure I understand your point. Why would we not mention, for example, the Wolf Effect, which consistently refers to "redshift", and is not only demonstrated in the laboratory, but has been shown that under certain circumstance will also proudce a frequency-indpenendent redshift? Likewise scattering phenomenon which can be demonstrated, will redshift spectral lines? If I was researching 'redshift' why should I not be told that these various specific scattering phenomenon, tired light, and the Wolf Effect exist? We're talking about ONE sentence? How else would I discover that 'redshift' is connecting with, for example, Compton scattering? --Iantresman 14:36, 7 December 2005 (UTC)

You're right that the interaction of light with matter can cause a redshift in many different ways. You provided a long list in your proposal part (b), but that list is far from exhaustive. I'm reminded of the song "Roxanne, you don't have to put out the red light." Here's a woman who turns on a red light to advertise herself when the sun goes down. Analyze the spectrum near Roxanne's light and you'd see a redshift recurring every night. Now we have the sneaky-postdoc-effect and the Roxanne-effect. Both are covered by the current introduction to the article along with light scattering phenomena and photochemical phenomena by including the sentences "The terms redshift and blueshift may be used without mathematical rigor to empirically describe the reception of altered wavelengths. The ratio describing redshift may also be used in a variety of situations that only apply to individual spectral lines or a subset of the spectrum." If redshift due to interaction of light with matter can occur in a huge number of ways then we can't list only the ones that are supposedly important to someone or refered to by more than 17 peer-reviewed articles or the ones you like best or something. Please try to read the current introduction with an open mind. I think it really does address your first proposal (a) in a concise way that would be impossible if we tried to tackle (b). How would you discover that redshift is connected with Compton scattering? By learning about Compton scattering. Flying Jazz 03:52, 8 December 2005 (UTC)

Some observations

First let me say that if one hears a chemist say "redshift" they will nearly never mean astronomical redshift and frequently mean Raman scattering, which is a common diagnostic tool in some branches of chemistry. So, yes, from a purely factual perspective there are scientists who say "redshift" and routinely mean something other than what this article is presently talking about.

Which may the crux of the problem. This article clearly centered on the astronomical redshift, so maybe it should be moved to astronomical redshift to discuss those observations and the possible explainations for them and then create a new redshift page that say something like:

Redshift refers to any one of a number of processes by which light can be moved to a lower ("redder") frequency. The astronomical redshift refers to a set of observations that ... Common causes for redshift in astronomy are ... Frequency shifting is also a valuable tool in diagnostic chemistry, where the most common causes of redshift are ...

However, just because I believe it would be appropriate to find a way to mention other uses of the the term redshift doesn't mean that one should stuff a laundry list of alternative views into an article on astronomical redshifts for the purposes of making the mainstream view appear scientifically controversial. Dragons flight 19:18, 3 December 2005 (UTC)

Dragons flight's suggestion has merit and while it may not put a complete end to this controversy, it would be a move in the right direction. DV8 2XL 19:48, 3 December 2005 (UTC)

I would agree with Dragons flight's suggestion if I could find a reference to a chemist text that used redshift in such a fashion. As it is, I cannot find any such reference. The closest we have are Joke137's citations above. None of those are chemist papers, though. Can either of you point me in the direction of somebody using "redshift" and not "red shift" in regards to Raman scattering? We could put the Raman scattering disambig on the Red shift page which is linked from the top. --ScienceApologist 02:08, 4 December 2005 (UTC)

Here [23]. Links 4, 5, 7, 8, and 9 are published papers using Raman "redshift". Most of the others look like preprints of papers, and I'm sure there are many more in the other 600 links. Dragons flight 02:24, 4 December 2005 (UTC)

Well, it looks like we're narrowing in on the culprit here. I am now firmly in User:Dragons flight's camp. We need to have a decent disambig while avoiding what the appearance of scientific controversy. Should we perhaps make the disambig on the top larger? We could make this page a different name, but there are a lot of articles that dynamically link here. I think this has taken us on the right path. --ScienceApologist 02:37, 4 December 2005 (UTC)

" ...a proportional increase in the wavelegnth of an electromagnetic wave. This is a definition that can be found in any introductory physics or astronomy text dealing with the subject of redshift." I found definitions limited to Doppler redshift only, and I found definitions limited to frequency independent wavelength increases, but I didn't find any definitions specifically mentioning and excluding frequency dependent wavelength increases. Did you find any? Thus, I found no guidance from formal definitions. The common usage of the term was quantified by Joke137's statistics, which show frequency dependent redshifts often enough to be mentioned in an article with 15,146 characters.

My point wasn't that there was an exlusory definition but that the definition of redshifts that was given never included frequency-dependent effects and indeed with further discussion excluded it by referring to the mathematical definitions we have on the page. --ScienceApologist`

"There is currently a section in the article that outlines the points made by those who are involved in nonstandard cosmology." But as I understand it, frequency dependent redshifts can't account for the redshifts of distant galaxies, so frequency dependent redshifts and nonstandard cosmology are two separate subjects.

Yes. That is why I propose to disambig at the Red shift page if there are no objections. --ScienceApologist 14:30, 4 December 2005 (UTC)

"...a minority pseudoscientific position..." If so, then sometimes a scientific attitude, like other virtues, is best taught by example, and maybe ScienceApologist's belated recognition will change things for the better. Art LaPella 07:43, 4 December 2005 (UTC)

Photochemist's opinion

First, let me say that I am not yet a professional scientist. I am an undergraduate doing an honors thesis in a photochemistry lab. We throw the terms redshift and blueshift around all the time to talk about changes in fluorescence spectra. We are referring to a chemical redshift, where the a polymer changes the wavelength at which it emits most intensely in response to certain experimental conditions. This redshift has nothing to do with the astronomical redshift. I have never seen a photochemical paper use the term redshift, and I'm strongly under the impression that it is an informal photochemical term, not one used in the literature. (However, being an undergrad, I'm not particularly well-read.) I would be happy to help develop an article on (photo)chemical redshift, if we decide to make this redshift a disambig. -- stillnotelf has a talk page 03:01, 7 December 2005 (UTC)

You make a good point that many fields use redshift in an informal way. Ian makes a good point too that many fields use redshift in a formal way but still without matching the mathematical definition that applies at all wavelengths. That other guy makes a good point that we should define redshift with mathematical rigor. I've added the statement "The terms redshift and blueshift may be used without mathematical rigor to empirically describe the reception of altered wavelengths in a variety of situations that only apply to part of the spectrum. However, most references to redshift—including the remainder of this article—utilize a mathematical definition that is uniformly applicable at all wavelengths." Having another disambig or additional articles on all the flavors of non-rigorous redshifts would be a mistake I think. Flying Jazz 06:54, 7 December 2005 (UTC)

The redshift equation is used by all scientists to work out the redshift of a single spectral line, regardless of the cause, and regardless of whether the redshift is Doppler-like or not. The redshift equation may be used as a rigorous definition, but it applies to an idea situation, in the same way that Boyle's law applies to an ideal gas. --Iantresman 09:10, 7 December 2005 (UTC)

Statements including the phrase "...is used by all scientists" are generally wrong. All scientists are not using mathematical definitions all the time. But you're right that the redshift equation may be used to quantify a redshift even in cases where it involves phenomena that apply to single lines or only part of the spectrum. Perhaps there are three definitions of the phrase. One is qualitative: "the light has experienced a redshift" requires no math. One is quantitative with application to a single spectral line or a portion of the spectrum. The most common definition is the one implying a uniform redshift over the entire spectrum. Your analogy to Bolye's Law is off base because Boyle's Law doesn't define anything and because (I think) it can be demonstrated in the lab that the Doppler-like effect of redshift really does follow the math as precisely as we can determine for huge regions of the spectrum while Boyle's Law can be demonstrated in the lab to always be an idealization of reality. I've edited the introduction to reflect these three possible distinctions. Flying Jazz 12:03, 7 December 2005 (UTC)

We generally don't use the given redshift equation at all, we just take the difference of two peaks. We're looking at the movement of peaks in a molecular spectrum, which doesn't have definable lines, but rather broad (dozens of nm wide) peaks. So, yeah, "single spectral line" never applies to chemical redshift, because molecules that shift colors don't have line spectra, and atoms (which do have line spectra) do not shift colors (that I know of). I don't want to get too embroiled in this, but like I said, someone please let me know if you decide you want a blurb on photochemical definitions of redshift. -- stillnotelf has a talk page 17:48, 7 December 2005 (UTC)

Yes please. Can you give (a) a descriptive definition of 'redshift', and if you use one, (b) a mathematical description too, (c) In a chemisty context, what cause or causes produce such a redshift. --Iantresman 18:03, 7 December 2005 (UTC)

I think Stillnotelf is talking about the fact that when a molecule changes its shape slightly due to a change in solvent or another molecule binding to it, peaks in its absorption spectrum will move a little. If an absorption peak moves from 300 to 350 nm then this might be called a redshift of 50 nm. The math is something like redshift = peak_wavelength_after - peak_wavelength_before. The cause is a different spacing of atoms in the molecule before and after a chemical or physical change. These values are an extension of the qualitative usage of redshift as any shift to a larger EM wavelength. Chemists want to know where to set the spectrophotometer so they aren't interested in the ratio. The oxygenation of hemoglobin causes a change from blue to red color because peaks in the transmittance spectrum of that molecule increase in wavelength. This could be called a redshift too. So could someone painting a house. Flying Jazz 06:22, 8 December 2005 (UTC)

Photochemistry added to article

I did a little research on photochemical redshift in addition to what I know already, and I added information on it to the article because there's a lot of science out there that assigns a length scale to something called a redshift. Stillnoteelf was right that IUPAC calls this usage informal. Nevertheless, I guess that IUPAC accepts it as proper usage for pure and applied chemists. See redshift here-- http://www.iupac.org/reports/1996/6812verhoeven/R.htm . My hope is that by explicitly stating definitions that are not formal and rigorous, the bulk of the article that uses the formal and rigorous definition will be stronger, and people who come here with the informal usage in mind will find what they came here for. Flying Jazz 22:51, 8 December 2005 (UTC)

I spoke with my advisor today - she tells me that she does indeed see "redshift" and "blueshift" in the literature, although some authors still prefer more formal terms. The link to bathochromic shift is perfect, because it keeps this article focused on more formal terms and redirects the chemistry discussion to a chemistry page. Thanks, Flying Jazz, I'd've probably gotten around to that in a week or two (I'm in the middle of final exams), but you made just the right link. -- stillnotelf has a talk page 01:42, 9 December 2005 (UTC)

I have updated bathochromic shift and its partner hypsochromic shift. Without wanting to open a can of worms, why is there no discussion over blue shift, and why is it titled in a different style? -- stillnotelf has a talk page 02:02, 9 December 2005 (UTC)

Red shift opens a can of Wikipedia worms because, as an astronomical observation, it is consistent with the Big Bang theory of origins but not with most other theories of origins that a few folks like better. If we observed blueshifts way out there in space then maybe we'd think we live in a collapsing universe...but more importantly the poor neglected Blueshift talk page would be getting all the attention! Flying Jazz 02:21, 9 December 2005 (UTC)

Oh, I understand the cosmology issues - I was just wondering why it's being ignored. I guess since it's rarer, it's less important. I notice that blueshift even re-uses the redshift graphic, even though the phenomenon should be reversed! -- stillnotelf has a talk page 02:38, 9 December 2005 (UTC)

That's a mistake. Thanks for pointing it out. --ScienceApologist

The meaning of proportional and its consequences

OK, this subsection is about math definitions for 12-year olds which a lot of very good scientists forget around age 23, but it appears to be critical for this debate. If a is proportional to b then a/b is constant. This means that the present article saying redshift is "defined as proportional to wavelength emitted" is incorrect. I've changed this to "redshift is defined as the proportionality between the change in wavelength and the wavelength emitted" which is correct.

This also gets to the heart of the deeper issue under debate. A proportionality is not just a ratio. A proportionality is an equality between multiple (at least two) ratios. If redshift is measured for one spectral line for the situations that Ian describes, we can say z=change/emitted and get a redshift. However, this is no longer a proportionality because there is only one ratio involved. Therefore it is a different mathematical definition of redshift (a ratio but not a proportion) even though the same equation is used to obtain the same a value with the same name. I don't think any of this should be in the article because it is esoteric minutae about the way science uses words and equations mixed in with 12-year old math. But I hope it clarifies some of the debate here and justifies my recent edits. Flying Jazz 13:15, 7 December 2005 (UTC)

Surely it's not esoteric minutae. Doesn't every redshift measurement begins as a measurement of a single spectral line. This is the more general use of the term. The special case is where full-spectrum prortionality is either assumed, or subsequently demonstrated. And then it's only astronomers who claim that the special case, full-spectrum redshifts are the only 'true' redshifts. Physicists studying scatting phenomenon, the Wolf Effect, tired light theories, do not. Indeed, the very fact that we have to qualify the word 'redshift' with a prefix (such as Doppler, full-spectrum, frequency-dependent, etc) demonstrates that the word 'redshift' is a general term, even though context may allows us to use it more specifically? And consequently, an article on 'redshift' should provide a list of the different kinds (and usage) of redshift. --Iantresman 14:48, 7 December 2005 (UTC)

The paragraph you wrote, Ian, is a unique point-of-view, but isn't based in fact. Claiming "general" and "specific" uses for redshift is like claiming that there are "general" and "specific" uses for energy since there are some scientists who use energy to mean things other than a quantity which has units of kg m² s^-2. The vast majority of physicists who would bother would define redshift as what we have currently on this page. --ScienceApologist 19:59, 7 December 2005 (UTC)

Some of my 500 references say otherwise. For example, when Wolf and James write [24]:

• "Fig. 2. Redshifts and blueshifts of a spectral line as predicted by (3.4)..." and,
  S_V(ω) = (2/R²) S_Q (ω) [1 + R_e μ_Q (P₁, P₂, ω)] (3,4)
• "It will be shifted towards the lower frequencies (redshifted)" (note their definition)
• "In one of the experiments the observed spectrum C was redshifted"
• "This expression shows that the relative frequency shift is independent of the central frequency ω₀ of the incident light and thus imitates the Doppler effect."

In other words, Wolf and James emphatically use 'redshift' in a DIFFERENT way to the fequency-dependent usage, and this demonstrates not only that a frequency-indepenedent redshift as the only definition is erronous, but examples should be given.

And yes, there are general uses of the word "energy". As you can see, I'm full of energy, as any dictionary will tell you, and I agree that physicists have a more rigorous definition too.

--Iantresman 10:46, 8 December 2005 (UTC)

general and specific

The terms "general" and "specific" are tricky here. On the one hand (maybe Ian's hand), there are more phenomena that can be related to a less rigorous definition of redshift (the qualitative observation or the ratio) than there are phenomena that can be related to the more strict definition (the proportionality), so the less rigorous definition is more "general." On the other hand (maybe ScienceApologist's hand), the less rigorous definition doesn't apply at every wavelength, so in this mathematical sense, it is more "specific" and only people who use the proportionality are using the "general" case. I think it's best to avoid the terms general and specific entirely in a situation like this. Flying Jazz 04:57, 8 December 2005 (UTC)

Ian's points

1) Every redshift measurement doesn't have to begin with the measurement of a single line. The bands in the color redshift next to the introduction could be apportioned among a group of undergrads. Each undergrad could measure the shift of one line all at the same time and then all the data could be collated simultaneously to find they all have the same redshift (or don't).

2) We don't have to qualify the term redshift with a prefix, but if someone comes across the term with a prefix and turns to wikipedia for help then the articles are already out there on doppler and compton and other phenonema for people to find out what the qualifier means.

Then the same argument should apply to Doppler-like redshifts. Recall:

• Wikipedia does NOT have a scientific point of view: "There is a minority of Wikipedians who feel so strongly about this problem that they believe Wikipedia should adopt a "scientific point of view" rather than a "neutral point of view." However, it has not been established that there is really a need for such a policy" [25].

• ".. articles should be written from a neutral point of view, representing all majority and significant-minority views fairly and without bias." [26]

In other words, if you mention specific examples of frequency-dependent redshift, then to be fair and unbiased, frequency-independent redshift should at least be mentioned too. There's perhaps half a dozen frequency-independent redshifts (plus the Wolf Effect which will also produce frequency dependent redshifts).

--Iantresman 10:46, 8 December 2005 (UTC)

I think you mixed up the words "dependent" and "independent" throughout that last post. Your statement that there are perhaps a half-dozen redshifts that don't use the proportionality at all wavelengths is just plain untrue. That number of half-dozen is based on subcategorizations that you want to make. The very good reason that the article doesn't discuss these redshifts is that there are not "perhaps a half dozen" of them. There are an unlimited number based on subcategorizations that other people want to make. Any event, process, or activity that increases EM wavelength could be called this type of redshift because "redshift" is being used as a synonym for "increase in EM wavelength". Why do you only want to select six and how will you justify the six you select and the millions you don't select? As for photochemistry, will you include redshifted peaks in transmittance spectra? The redshift in the transmittance spectrum of hemoglobin when it becomes oxygenated is what turns blood from blue to red. Will you include redshifted peaks in reflectance spectra? This is what happens when I paint my house a different color and when an octopus changes the pigments in its skin. Do these individual usages fall into your half-dozen or will you lump them into "photochemical redshifts" or will you lump photochemical and other redshifts into "non-cosmological redshifts"? Every subcategory of usage will have similar sub-subcategories.

This entire debate is about usage and semantics because that was what you asked for in your request for peer-review. I agree with you that non-proportional redshifts are still redshifts. These redshifts are mentioned in the introduction to the article now. But picking and choosing which non-proportional redshifts to discuss as examples will always be an exercise in non-neutral POV and will always be inherently biased. The neutral POV is to present all of them together in one category as is done now. Flying Jazz 14:40, 8 December 2005 (UTC)

• Surely painting your house red does not shift the frequency of light. Paint absorbs all but the red wavelengths. Likewise octpuses changing colours.

• Sorry to sound facetious, but I can't find any peer-reviewed usage of "house-paint redsfhift" nor "octopus redshift", nor to the alledged effect causing it. However, I do find frequent reference to Brillouin scattering, Compton scattering, Raman scattering and the Wolf Effect with regard to redshift. I don't find "dozens" of other kinds of frequency-dependent redshifts mentioned by name,

• The Wolf Effect, (a) produces an actual frequency-dependent redshift (b) may produce a frequency independent redshift that is indistinguishable from the Doppler redshift. See my extract immediately above the sub-head "general and specific". --Iantresman 17:15, 8 December 2005 (UTC)

Can somebody tell me under just what conditions the Wolf Effect does and doesn't give a frequency independent aka Doppler redshift? --Curious in Munich 20:08, 8 December 2005 (UTC)

You may only be reflecting the facetiousness that I may be emitting. Please read the first few sentences here about the redshift that occurs when cooking a lobster. http://www.ch.man.ac.uk/people/academic/RelatedDocuments/JRH/Lobsterphysicstodayoct2002.pdf

This lobster-cooking redshift (like angry-octopus redshift and painting-a-house redshift) is an example of a reflectance spectrum that has peaks at increased wavelengths. It's REAL! It's so real, your own eyes SEE it! The frequency of reflected light is shifted because the molecules in the material have been altered. Reflectance, transmittance, and absorption redshifts due to chemical change are three subcategories of terrestrial non-cosmological photochemical perhaps-biological perhaps-nutritional (insert adjective here) redshifts that don't involve emission. Then there are subcategories of photochemical redshifts that do involve emission and then there are a gadzillion other things that might not be photochemical redshifts but are other kinds of redshifts that might not be found in your abstract query from the Nasa Astrophysics Data System because there are no angry octopuses or cooked lobsters in space.

If you insist that I find peer-reviewed articles that use the term "reflectance redshift" or "angry-octopus redshift" or "biological redshift" then you are the one who is forcing this article into a scientific POV instead of a neutral one. Now it's time for me to cook a steak. I like my steak medium-well. Here's a test question for anyone who might be following along. Does cooking a steak cause a redshift or a blueshift in what my eyes see and do I need to consult a peer-reviewed journal to know when it's done just the way I like it? Flying Jazz 18:35, 8 December 2005 (UTC)

3) I didn't mean to imply that certain usages of redshift were minutae. I added these usages to the introduction of the article because I agree with you that they occur often and are NOT minutae. I meant that this debate about semantics and word-usages is minutae. Still important to have I guess.

My argument is that the introduction as it is now provides a list of the different usages of redshift. Usage 1 is qualitative. Usage 2 is a ratio. Usage 3 is a proportion. This satisfies your proposal (a). I think your proposal (b) is not so much about word usage as it is about selecting some of the many physical processes that involve word usage 1 and/or 2 (but not 3) as more important and more "listable" than other physical processes that do the same thing. Flying Jazz 04:57, 8 December 2005 (UTC)

It seems that the article is becoming less to do with Doppler-like redshifts, and more to do with the variety of uses of the term redshift in science. But I think that if we mention "bathochromic shift" we ought to give examples, just as we do with Doppler-like redshifts. For your average person, "bathochromic shift" means nothing; but pigments in lobsters changing colour (if indeed this is related), gives people something to relate it to. --Iantresman 22:37, 8 December 2005 (UTC)

You might be right. The bathochromic shift article could be spruced up a bit. As for the redshift article, my main purpose in adding photochemical usage is to add clarity so readers know what formal redshift isn't. Giving examples of bathochromic shift in a redshift article would be pretty dumb when there's a bathochromic shift article out there already ready and waiting. Flying Jazz 22:59, 8 December 2005 (UTC)

There's already a Gravitational redshift article page, so why not a Doppler redshift article, and Cosmological redshift article, or even "Doppler-like redshifts" page? I still think this Reshift page should be comparing and constrasting all types and possible causes of redshift, and not detailing Doppler-like redshifts. We are readily discussing "Non-Doppler-like redshifts", but where do I find out what this means? Why do people discuss Brillouin scattering and the Wolf Effect in the context of redshift? What is the significance of 500 peer reviewed articles that mention non-Doppler-like redshifts? If I go to the page on, for example, Galaxies there is little detail on any paricular galaxy, or type of galaxies; but at least I can find out what options there are. --Iantresman 23:25, 8 December 2005 (UTC)

I've already addressed these questions once because I took them seriously. See #2 in the discussion above. Now I'm starting to realize that they may just be rhetorical questions to you because when I answered them up there you just started asking them again down here. Flying Jazz 00:27, 9 December 2005 (UTC)

At the time that the questions were answered originally, there was no bathochromic shift mentioned in the article. Now that this has been added, it seems reasonable to wonder why mention of Brillouin scattering, Compton scattering, Raman scattering, the Wolf effect, and other theories such as tired light theories, are still excluded? The Wolf Effect, for example, has NOTHING to do with bathochromic shifts, NOTHING to do with scattering, but will also produce a redshift. --Iantresman 08:41, 9 December 2005 (UTC)

Redshift and Arp

This page has a section titled "Redshift interpretations in non-standard cosmologies" - That section is a perfectly valid place to put the following summary of Arp's interpretation of redshift:

Another critique of the standard interpretation of cosmological redshift has come from Halton C. Arp, who has claimed to find empirical support in the existence of apparently connected objects with very different redshifts. Arp has interpreted these apparent connections to mean that these objects are in fact physically connected. He has further hypothesized that the higher redshift objects (usually Quasars) are ejected from the lower redshift objects - which are usually active galactic nuclei (AGN). In Arp's model the large observed redshifts of these objects is dominated by a non-cosmological (intrinsic) component. Conventional cosmological models regard these as chance alignments and Arp's hypothesis has very few supporters within the research community.

Before I re-insert the paragraph I will wait for specific comments by others that actually have demonstrated a neutral POV on this page with regard to the neutrality of the paragraph. Joshua Scroeder's opinion is not the final say on this matter and I will not defer to it. Wikipedia is supposed to be a worldwide community resource and it is absurd that a single individual is persistently allowed to vandalize the efforts of others.

Personal attacks aside, my problem with the paragraph is that it gives a lot of credit to Arp without making it clear that a) his research is based on limited observations and has its roots in the quasar controversies of 30-40 years ago, b) why do you include a sentence about ejection and physical connection of quasars when the article is about redshifts? Isn't this a bit of a red herring? c) is there anything wrong with keeping the nonstandard section very short and having people who are interested link over to that article?

-ScienceApologist 02:29, 4 December 2005 (UTC)

Gives Arp a lot of credit? The paragraph includes the following phrases: "has claimed to find", "has interpreted", "has hypothesized" - and the paragraph concludes with a statement that he has very few supporters in the research community. You can't get any more neutral and factual than that. Its a simple statement of what he says and why he says it.

In response to your lettered points:

(a) The quasar controversy has been going on for 40 years. And the inclusion of the last sentence makes it clear that in that 40 years, he has gained very little support from other researchers.

When is the controversy going to be over? Arp doesn't seem to want to admit that he has been wrong about anything. Observations of host galaxies don't even seem to phase him. I don't accept that this is an ongoing controversy anymore than the Shapley-Curtis debate. --ScienceApologist 18:51, 5 December 2005 (UTC)

(b)First, the ejection is part and parcel of Arp's interpretation about redshift. Since the article is about redshift a sentence stating why he has concluded that there are intrinsic redshifts is necessary for context. But if we want to apply your criteria, then we should toss out the whole section on expansion of space - because the "article is about redshifts" - not about expansion of space.

Arp's critique represents an arguably narrow part of the entire redshift phenomenon. It applies only to Arp quasars. This seems a bit myopic for a broad article on "redshift" in general. --ScienceApologist

(c)Again, by that criteria, we should make the expansion of space section very short and refer people to the Big Bang or an entirely separate expansion of space article.

No, I think we should give in to notability in how something is reported. How notable is Arp compared to the Big Bang? --ScienceApologist 18:51, 5 December 2005 (UTC)

It is inconsistent of you to make arguments such as those in b and c but not apply the same argument to the portions of the article you like.

And you have to keep in mind that while Arp disputes the Big Bang, there are advocates of intrinsic redshift that think intrinsic redshifts are a phenomenon superposed upon the cosmological redshift from expansion. Those ideas would be most appropriate in this article. There really should be a section on Causes of redshift and another section on Alternative proposals for causes of redshift. --DavidRussell 15:18, 4 December 2005 (UTC)

What I don't understand about the comparison of intrinsic redshifts to a metric expansion is that an intrinsic redshift component smacks of unfalsifiability. It isn't a model for redshifts but it's an argument that there are other mechanisms for redshift that haven't been discovered yet. There is no formula to point to that describes an intrinsic redshift. This is different from the expansion of space which directly relates the scale factor to the redshift.

Reporting Arp here in an entire paragraph gives him proportionally more space than that which he is generally dealt with by those who study the phenomenon. I'm not convinced that Arp's ideas represent a significant enough of a minority to be portrayed in this way on this page. This is an editorial opinion, of course. --ScienceApologist 18:47, 5 December 2005 (UTC)

As a digression from our current RfC, I think this is quite an interesting point, but in a slightly wider context. Reading the redshift article, I note that the cosmic microwave background radiation has a redshift value of z = 1089. It would also seem to make sense that this redshift may be a commbinations of (a) Cosmological (b) Doppler (c) Gravitational (d) Other unspecified Doppler-like mechanisms. Since all possible causes are indistinguishable, is it possible to (a) estimate the proportion of each cause (b) Falsify anyone of them as contributing to the overall redshift? And then having said also this, isn't this very discussion of "intrinsic redshifts", whether real or not, a very real area of discussion, in which case a cursory summary of (a) why it is considered, and (b) rejected, must be worthy of comment? --Iantresman 19:06, 5 December 2005 (UTC)

Yes: (a) Cosmological. Almost 100%. (b) Doppler: 10⁻³. It is mainly responsible for the dipole, due to the peculiar velocity of Earth (c) Gravitational. Arguably the same as cosmological, but the Sachs-Wolfe effect is the main source of gravitational redshift. Probably about 10^-5. (d) None that I know of. There is a very carefully worked out theory that agrees with the data for all these. –Joke 03:27, 9 December 2005 (UTC)

Arp has been reinstated pruned down and ready for action. I'm not convinced we should include him, but in fairness to the fact that Zwicky's Tired Light gets a mention it's only fair that Arp's pathological skepticism gets a mention as well. --ScienceApologist 07:55, 9 December 2005 (UTC)

Red shift or redshift?

In astronomy, redshift is most often used, but "red shift" is also acceptable. What is it like in chemistry? Do the chemists use "red shift" or "redshift" more often? This is of vital importance to the disambiguation. --ScienceApologist 02:43, 4 December 2005 (UTC)

I am not a chemist, but I believe the situation there is the reverse, that "red shift" is most common but that "redshift" and "red-shift" are acceptable alternatives. Dragons flight 04:16, 4 December 2005 (UTC)

From what I can gather this is true. So perhaps the disambiguation should go on the Red shift page instead of here? We already link to this page at the top of the article. We can just make it clearer that this is the redshift associated with astronomy. --ScienceApologist 04:19, 4 December 2005 (UTC)

Redshift proposal clarification

I just wanted to clarify what is being proposed. The way I read the suggestions is as follows:

1. The current Disambiguation page, "Red shift" (two words), summarises scientific and non-scientific uses of the word Redshit and redshift, pretty much as it does now.
2. It is proposed that the current page on "Redshift" becomes a Disambiguation page summarising scientific uses of the word redshift such as (a) Astronomical (Doppler-like) redshifts (b) Non-Doppler-like redshifts (c) Any other scientific uses of the word redshift.
3. It is proposed (by Dragons flight's) that a new page be created called something like "Astronomical redshift", which will describe all Doppler-like redshifts.

To which we should add that:

• All scientific redshift pages should include a fair and prominent mention to the other redshift pages. eg. The Astronomical redshift page would mention something like "See also other scientific uses of the term redshift.

--Iantresman 10:42, 4 December 2005 (UTC)

The proposal I laid out is different: disambig on the Red shift page and expand the dynamic disambig link at the top of this page. --ScienceApologist 14:26, 4 December 2005 (UTC)

As I see it, there are now three options on the table:

1. My original Request for Comments described above

2. Dragons flight's suggestion of a compromise "Astronomical redshifts" page, as I have described in the section "Redshift proposal clarification".

3. And now your suggestion to expand the existing "Red shift" Disambiguation page.

The problem I have with the last suggestion is that the use of the term 'redshift" as used by scientists in peer-reviewed journals regarding Brillouin scattering, Compton scattering, Raman scattering, the Wolf effect, neutrino redshift, and other theories such as tired light theories, tend to use the word 'redshift' without a space.

--Iantresman 15:17, 4 December 2005 (UTC)

Actually, there seem to be more articles that use "red shift" with the space in terms of the Raman scattering, for example. The chemists that use "red shift" in this sense are referring to a "shift to the red". That's not to say there are no examples of chemists using "redshift", just as there are examples of astronomers using "red shift". It's simply a matter of what seems to be common practice. If we could get an optical chemist to weigh in, that would probably be the best. --ScienceApologist 15:49, 4 December 2005 (UTC)

Raman scatting is just one cause out of several others mentioned. Looking at Google Print, I find:

• "Compton Scattering" + redshift = 133 refs 10-fold usage over + "red shift" = 13 refs
• "tired light" + redshift = 65 refs 9 fold usage over + "red shift" 7 refs
• Brillouin + "redshift" = 5 refs slightly less than + "red shift" 8 refs
• "Non-cosmological redshift" 11 refs exclusively over "Non-cosmological red shift" [0 refs]
• "Intrinsic redshift" 55 refs almost exclusively over ::::*"Intrinsic red shift" 1 ref

So whereas Raman and Brillouin scattering seems to use "red shift" slightly more than "redshift", all other uses I've mentioned heavily use the single word "redshift". --Iantresman 16:40, 4 December 2005 (UTC)

This confirms what I suspected. Compton Scattering as a mechanism for redshift is promulgated by one disgruntled, retired NASA scientist and isn't studied outside of this. Tired light is Zwicky's idea, and intrinsic/non-cosmological redshifts are all Arp promotions. Since Birllouin and Raman scattering are well-known as the "other sort" of red shift, I say we include them on the red shift page. That removes them from discussion here.

Now we need to discuss the notability of Compton-scattering, tired light, intrinsic redshifts. The section at the bottom of the page should cover that.

Does this satisfy? --ScienceApologist 17:12, 4 December 2005 (UTC)

As far as I can tell from the previous discussions:

• The only person in favour of your proposal is yourself.
• The only person in favour of your defintion of redshift is yourself.
• The only person who does not accept other uses of the term redshift (except in respect to Raman scatting) is yourself.
• The only person who rubbishes 500-peer reviewed references to other uses of redshift (except in respect to Raman scatting) is yourself.

But the original Request for Comments is still in its early days yet, and I anticipate at least some criticism of my proposals from someone other than yourself. --Iantresman 18:01, 4 December 2005 (UTC)

Perspectives

The issue here is the definition of redshift. I see no reason for any particular controversy here. Use of the term "Redshift" in science literature predominantly refers to astronomical redshift, this is pretty obvious. In astrophysics, the cause is mostly assumed to be cosmological, i.e. Hubble expansion. This is also not in dispute. However, other uses of the phenomenon in science are notable and should be included.

Redshift is a shift (towards the red) in the absorption or emission spectra of a light source, when compared to fixed well-known chemical spectra. The term was first used in astronomy and astrophysics, where it almost always refers to galactic redshift and is assumed to be caused by expansion as inferred by the Hubble relation ... blah blah. This is not in dispute, regardless of whatever your personally preferred explanation for the observed redshift is.

However, redshift has also found applications in other fields, such as analytical chemistry. Subsequent investigations have found several physical and chemical processes that can cause redshift in materials, some of which are frequency dependent. Such effects are ... blah blah.

Given this, I'm not sure what the fuss is about. I don't think we need a separate Astrophysical redshift page, if people are willing to be sensible. Sadly, there is one troublemaker here on some strange personal vendetta. Jon 08:44, 5 December 2005 (UTC)

There are a few nitpicks I have with your comments:

1. Redshift is not always cosmological. It is sometimes due to gravitational or Doppler velocities as shown in the article.
2. Redshift is a shift to lower frequency not just "toward the red". I'm assuming you know this though and just glossed it over. However, it's important we get it right in the article.
3. The redshift term does not "almost always" refer to galactic redshift. In cosmology it may, but there are plenty of stellar astronomers who never refer to galactic redshifts.
4. The redshifts in analytical chemistry are often termed "red shift" with the space. As such, why not include those on the disambig page?
5. That Iantresman is on some strange personal vendetta may be true, but that's beside the point.

ScienceApologist 08:57, 5 December 2005 (UTC)

I was glossing somewhat. Unfortunately I was talking about you, but I'm assuming you have a wry sense of humour. In particular, what is your problem with mentioning non-astrophysical redshifts? The current article launches straight into astrophysics without first covering a general definition.

I remember from my geochemistry that redshift came into XDF analyses. Interestingly, while searching for crystallogrphy and redshift, I came across this curiousity - Arxiv which is probably not hugely relevant yet still interesting. Jon 09:04, 5 December 2005 (UTC)

I have no problem mentioning analytical chemistry red shifts whatsoever. However, as I pointed out above, I think they more often use "red shift" as opposed to "redshift". --ScienceApologist 09:12, 5 December 2005 (UTC)

I think it's a mistake to put too much emphasis on the presence or absense of a space. I think we have seen that the usage is not universal, neither is it logical, and I wouldn't count on a Wiki reader choosing the right one. That might mean redirecting from "Red shift" to "Redshift" and sorting out the other issues with one page less, but I don't have a comprehensive suggestion so I'll duck and cover again. --Art Carlson 10:33, 5 December 2005 (UTC)

I think Wikipedia needs a pub. Everything gets settled one way or another at a pub. - RoyBoy ⁸⁰⁰ 17:44, 5 December 2005 (UTC)

I agree, make mine a double Jon 00:52, 6 December 2005 (UTC)

Criticism

From above:

Incidentally, the page has been updated with good figures but a poor text edit which removed much of the clarity and rigour.--Serjeant 16:45, 5 December 2005 (UTC)

Ouch. Can you point to an example? --ScienceApologist 19:04, 5 December 2005 (UTC)

OK. To be fair the graphics are really very good - I just have a problem with some of the new text. Here are some quick comments, working down.

The first comment is one of style. The article starts out with a lengthy description of the context of redshift; I believe it should immediately define the thing (with an equation). Context can come later.

In the causes section, it starts by suggesting that the expansion of space "creates new space between the source and the observer". This is incorrect, and in any case contradicts expansion as described - is it stretched old stuff or new stuff?

Good catch. The sentence has been reworded. --ScienceApologist 18:57, 6 December 2005 (UTC)

A bit further down, the Doppler effect is described using a Taylor series, which is by definition approximate. This is an encyclopedia definition, so either the full equation or the low-v limit should be quoted.

Full equation instated. Low-v limit quoted. --ScienceApologist 18:57, 6 December 2005 (UTC)

Much nicer :) --Serjeant 19:34, 6 December 2005 (UTC)

In the next section we have "metric expansion of a vacuum can occur faster than the speed of light". Later we have "the effect is Galilean invariant with physical movement of the galaxies". Both of these are pretty nebulous if they mean anything at all.

The first comment I think is important considering the present dark energy issues of expansion and also cosmic inflation. Perhaps it should be reworded with reference to horizons?

I completely understand your enthusiasm to communicate exciting advanced ideas, but we must avoid losing the reader. To do this carefully and rigorously we would need to introduce too many extra concepts, such as proper distance (as opposed to comoving), time-like hypersurfaces and so on. In the interests of succinct and accessible definitions, perhaps it's best to say simply that distances increasing due to expansion of space is a physically different situation to things moving inside that space. There's nothing stopping us linking to other pages though.-Serjeant 19:34, 6 December 2005 (UTC)

I think I agree with this, however since we quote redshifts that are far greater than 1 there is a natural tendency for people to ask the question of how you can get velocities faster than the speed of light. --ScienceApologist 18:33, 7 December 2005 (UTC)

I'm not sure why you think the second comment is nebulous.

The situation is better described by the original text: "Nevertheless, astronomers (especially professional ones) sometimes refer to 'recession velocity' in the context of the redshifting of distant galaxies from the expansion of the Universe, because they all know it's only an apparent recession. This can sometimes be confusing to the intelligent lay person who does not realise the astronomers are just talking in a shorthand, and aren't in fact ascribing this redshift to a real recession movement of the source."--Serjeant 19:34, 6 December 2005 (UTC)

I think that this statement is a bit weasely and slanted. For one, it bifurcates the population into intelligent lay people (who defines their intelligence) and "the astronomers" who form a cadre of jargon-using closed-shop misers of terminology (a characterization that Iantresman may agree with, but isn't NPOV). Anymore, most cosmologists I know don't speak of the Hubble Flow as representing a recessional velocity since the scales have increased enough to allow for redshift space up to 6,7,(10). Recessional velocities in those instances make little physical sense. Recessional velocities tend to be used when referring to high velocity clouds, for example. In those cases, they are due to actual recessional velocities and not the Hubble Law. Maybe we should dispense with the connection between the Hubble Flow and recessional velocities altogether. --ScienceApologist 18:33, 7 December 2005 (UTC)

All disciplines, including astronomy, have techincal terms which use words in a more specific and restricted sense than their general use outside the field. This is a genuine bifurcation, as you put it, and it is not in any sense contentious to portray it as such. I'm afraid you're mistaken if you think professional astronomers never use the term "recession velocity" in the knowledge that it is not Doppler. It is even implicit in the term "Hubble flow"; this "flow" is clearly not a flow, but no professional is confused.--Serjeant 15:34, 8 December 2005 (UTC)

I think what I'm trying to say is that the distinction may be broader than the sentences you proposed. Astronomers say a lot of things about redshift space in different contexts. I wasn't claiming that astronomers "never use the term", only that it has started to fall out of use a lot more in the last decade or so. --ScienceApologist 20:36, 8 December 2005 (UTC)

--ScienceApologist 18:57, 6 December 2005 (UTC)

Further down, space is not expanding DUE TO a time dependent scale factor. The latter is a description, not a cause.

I disagree. I think the Friedmann Equations provide a cause for space expansion by allowing for a scale factor. If general relativity didn't describe cosmological scales, we would have no notion of expanding space. --ScienceApologist 18:57, 6 December 2005 (UTC)

So the time dependent scale factor causes the expansion of the Universe? I still contend that the former describes the latter, rather than causing it. The causes of the expansion of the Universe are better given as the initial conditions (but what caused them?) combined with the requirement of obeying the Einstein field equations.--Serjeant 19:34, 6 December 2005 (UTC)

Well, it depends on whether you think that "due to" implies causality and whether causality is in the sense of the arrow of time. The redshift of light is due to the scale factor in the same way that the ratio of force to acceleration is due to the inertial mass. Isn't this a bit nitpicky? Inflationary theory, of course, demands a scale factor as the (roughly) linear remnant of the inflaton exponential expansion and in some sense can be thought of as the set for "initial conditions". So is this statement really so problematic? ScienceApologist 18:26, 7 December 2005 (UTC)

"Due to" can easily be taken to mean a causal link. In any case, the article is not saying that redshift is "due to the [changing] scale factor", but that space is expanding due to the scale factor, which is tautological. Really, the phrasing needs a lot more care I'm afraid.--Serjeant 15:34, 8 December 2005 (UTC)

But tautology is often employed in physics vis-a-vis Newton's Second Law. How would you rephrase it (or would you simply omit it)? --ScienceApologist 20:36, 8 December 2005 (UTC)

Then it describes "a coordinate shift in the electromagnetic wave to lower energies". Have we just moved into phase space?

Perhaps poorly worded. I'm not sure how to reword it though. --ScienceApologist 18:57, 6 December 2005 (UTC)

It's not a coordinate shift (transformation?).--Serjeant 15:34, 8 December 2005 (UTC)

How is it not an affine transformation? --ScienceApologist 20:36, 8 December 2005 (UTC)

It's not a coordinate transformation in the sense that GR uses the term; i.e., it's not referring to choices of reference frame. You're right that you can, somewhat imaginitively, regard all physics as a mapping of a past phase space position onto a future phase space position. When this mapping is linear, you can call it an affine transformation. However this is taking us well outside the realm of defining redshift in the most accessible and accurate way. I think we would be best keeping to the conventional use of "coordinate transformation" in the context of general relativity.--Serjeant 10:27, 9 December 2005 (UTC)

"Such an effect is exactly analogous to a redshift caused by a recessional velocities that increase with the distance away from the observer." Plain wrong, I'm afraid.

There are subtle differences, but I think saying that this statement is "plain wrong" is a bit overkill. How would you modify it? --ScienceApologist 18:57, 6 December 2005 (UTC)

It's different; therefore it's not "exactly analagous". It's nothing to do with overkill , it's about an encyclopedia entry being correct.--Serjeant 14:35, 8 December 2005 (UTC)

If we remove "exactly" does that satisfy? --ScienceApologist 20:36, 8 December 2005 (UTC)

My feeling is that we would be best avoiding all claims of analogy between space expansion and Doppler shift.--Serjeant 10:27, 9 December 2005 (UTC)

That's about as much as I have time to do for now. I don't want to sound like we shouldn't be grateful for people putting in their time for free for the public good here, but at the moment we have an article which has quite a few loose ends. The figures are super though.--Serjeant 15:13, 6 December 2005 (UTC)

I'd like to disagree with one point. I don't think the article should start with an equation.

1. Wikipedia is aimed at all, not just scientists. Equations mean nothing to the vast majority of people.
2. Redshift primarily is an observation; I think that's the one thing everyone agrees upon: a movement of a spectral line. Its alledged causes, and formal description using maths are secondary.

--Iantresman 15:22, 6 December 2005 (UTC)

The redshift entry in my old Penguin Dictionary of Physics has a two-sentence description in words, then a less ambiguous algebraic definition of the same, which seems the right balance to me. I'm afraid that most knowledge of the physical universe is closed to someone for whom equations mean nothing at all.--Serjeant 15:31, 6 December 2005 (UTC)

Exactly. Description first, maths later. And arguably the maths only quantifies the redshift, it says nothing about the cause, nor how the phenomenon manifests itself. --Iantresman 17:01, 6 December 2005 (UTC)

Both of which can come later. The equations should come very early on because they are the most succinct and unambiguous definition.--Serjeant 18:19, 6 December 2005 (UTC)

Wikipedia:WikiProject Physics

I just found the RFC associated with this page. A really good place to announce such things, and ask for help, is at Wikipedia talk:WikiProject Physics. That is the place where most of the physicists hang out, and in particular, the people with the PhD's. However, you don't need a PhD to participate -- its just a good place where physics topics can be discussed and announcements/requests can be made. linas 06:14, 8 December 2005 (UTC)

NPOV removal

Since we've resolved the issues with respect to photochemistry (which umbrellas Raman scattering, Brillouin scattering, etc) and we've established a consensus intro, the NPOV tag is not appropriate. --ScienceApologist 07:12, 9 December 2005 (UTC)

I've restored the Neutral Point of View tag. As far as I can see, we're still in the middle of a Request for Comments. I disagree that we have developed a consensus intro. We have had some great discussion and contributions from FlyingJazz, yet we have completely ignores support from Harald88, David Russell and a contribution from Eric Lerner. --Iantresman 08:41, 9 December 2005 (UTC)

Being in the middle of an RfC does not mean that the NPOV flag needs to stay. The NPOV flag should come down when it is clear there is no longer an issue of NPOV. So far, I have not seen any indication that there are any outstanding issues. --ScienceApologist 08:45, 9 December 2005 (UTC)