Talk:Redshift/Archive 10

This is an archive of past discussions about Redshift. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Archive 5

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Archive 8

Archive 9

Archive 10

Archive 11

Title and spinoff problems

Obviously the concept of redshift really can't be discussed without including blueshift, which this article does in everything except title - instead giving a separate stub to Blue shift (note the inconsistency of style between redshift and blue shift). To fix this I propose renaming/moving this page to something like redshift/blueshift, red/blueshift, etc. and redirect any old pages like blue shift. Anynobody 04:54, 26 May 2008 (UTC)

Or alternatively we could merge and redirect blue shift here. The general wave phenomenon is covered at Doppler effect. Using the Redshift title has the advantage of simplicity and, at least in my limited experience, covers most instances of Doppler-shifted light. If I recall correctly, we should avoid using the solidus in article titles since that denotes subpage.

It is not true that for every red shift there is a blue shift. They cannot all be merged; the discussion becomes chaos.

Perhaps three different redshift pages should exist, named, say,

1. Hubble Red Shift

2. Radar and Lidar Red and Blue Shift

3. Gravitational Red and Blue Shift.

That way, persons wanting to add material on blue shift could do that on pages discussing phenomena that actually do manifest blue shift. They would not have to add blue shift comments to pages where blue shift is not a subject. SyntheticET (talk) 20:54, 23 October 2008 (UTC)

Energy considerations

Since the expansion of the universe leads to a red shift, it also indicate a loss of energy. Photons from the recombination and mater/antimater annihilation in the early universe must at one time have made up a great part of its energy. Now, through cosmological redshift, most of that energy appear to be gone. How is that possible? —Preceding unsigned comment added by 83.254.79.14 (talk) 22:19, 29 May 2008 (UTC)

General relativity. Energy conservation in GR. ScienceApologist (talk) 23:17, 29 May 2008 (UTC)

Additional Mechanism

Now is an appropriate time to include in the MECHANISMS section, mention of Wave Decay theory. Wave decay had been proposed by Edwin Hubble and his co-workers around 1900 A.D. soon after discovery of the spectroscopic shift toward longer wavelengths that was named after him. The controversy was obviously political to astronomers. Hubble withdrew from wave decay and assumed the position demanded: the cause was at that time unknown. If it had been sought after the discovery of the quantum by Max Planck, a wave decay equation would probably have been written in the 1920's. As it was, the world was just out of one war and facing another.

In 1957 Expanding Universe and Big Bang theory became politically important and then urgent. Once dismissed as "tired light", wave decay was taken out of circulation after In high school physics it had been stated in 1958 that as for tired light, "no mechanism has been found." That does not preclude the determination of such a mechanism now, in the new millennium.

It is sensible by now, over half a century later, to consider wave decay theory a serious contender. This is not a contest for the throne. At least one mechanism already exists in the form of an equation that appears to describe the Hubble Red shift accurately. SyntheticET (talk) 20:01, 23 October 2008 (UTC)

blue shift

Why is blue shift redirected here? There is no mention of it here. 70.51.9.237 (talk) 11:34, 9 July 2008 (UTC)

It's mentioned 26 times, for instance at the end of the first paragraph. A blue shift is about the same as a redshift, but in reverse, so the same explanation applies. The article is called "redshift" not "redshifts and blue shifts" because cosmic expansion causes a redshift, not a blue shift. Art LaPella (talk) 23:08, 9 July 2008 (UTC)

Mechanism text

The following text was added well-intentioned, but awkwardly:

A redshift can be measured by looking at the spectrum of light that comes from a single source (be the analyzed, unknown source called _X) (see idealized spectrum illustration top-right). If there are features in this spectrum such as absorption lines, emission lines, or other variations in light intensity, then a redshift can in principle be calculated. This requires comparing the observed spectrum of _X to a known spectrum (be the known source called _A) with similar features. For example, the atomic element hydrogen, when exposed to light, has a definite signature spectrum that shows features at regular intervals. If the same pattern of features (imagine a chart on which the wavelength is represented on the horizontal axis, and on which the intensities of light at different wavelengths are represented vertically. The curves, lines, spikes etc. formed on this chart would be unique and probably distinguishable for each element) as on spectrum of _A (in this example, hydrogen) is observed in another spectrum - the spectrum of _X - with the only noticeable difference being that of a shift in wavelength, then _X could be identified as _A, and a redshift could be determined for the object _X.

Aside from the _A and _X awkwardness, there seems, to me, to be a problem with describing an image that we don't have. This would be a good image to produce and include in the text, and I encourage a motivated editor to make such an image. However, I don't think that making a textual abstaction as such is helpful for the reader, and giving these abstractions arbitrary lables _X and _A is doubly confusing.

--ScienceApologist 12:56, 29 December 2006 (UTC)

I agree on the awkwardness of the paragraph. We do have an image that precisely shows what's going on -- at the head of the article. It might be nice to go into more detail on how redshifts are measured using lines, but I think this is confusing. Sdedeo (tips) 18:14, 29 December 2006 (UTC)

It's a bit confusing for some people who may think that it is just the lines themselves that are shifting and not the entire spectrum (continuum and all). It might be a good idea to get the plots of the spectra of two different galaxies at different redshifts to show the shift of the continuum and the lines. --ScienceApologist 01:08, 2 January 2007 (UTC)

Ordinary exponential decay of waves is found in almost all cyclic phenomenon on Earth. It is extremely well known in water waves, the vibration of springs, and other kinds of oscillatory phenomena. Reasonable grounds exist for the idea that the difference between adjacent manifolds cannot be made absolute in general relativity, because of uncertainty between them. It is displayed in macroscopic form in the Klein Bottle, which illustrates that the difference between the interior and exterior of any closed domain is not absolute. In this way, the energy and time domains within the photon's quantum are not absolutely distinct. The high energy of a freshly emitted photon gradually flows, through the not-quite-absolute manifold separating it from the time domain within the same photon, and that is a sufficient basis for exponential decay sufficient to explain the Hubble Red Shift. Even the magnitude of the uncertainty between the two domains is already known. It is the Planck action quantum. A document describing that is on the internet. SyntheticET (talk) 18:34, 4 May 2009 (UTC)

clarification of shifts

It is very important in this discussion to keep the different kinds of spectral shift distinct. More than one kind of spectrographic wavelength shift exists in nature. They are all fundamentally different in one or more of the important fundamental dimensions of physics.

1. Velocity or Doppler Shift can be a shift toward longer or shorter wavelength depending on the direction of motion relatively toward or away from an observer. Doppler Shift is widely used in radar for determining vehicle speeds, as at traffic control cameras.

2. Gravitational frequency shift is also a shift toward longer or shorter wavelength depending on the direction of motion, whether rising or falling from the gravitationally massive object. Gravitational red shift is observed in the Sun's spectrum and in spectra of other, massive stars.

3. Hubble Red Shift always appears as a shift toward longer wavelengths. This is observed only in light from extremely distant objects, mostly galaxies beyond 50 million light years distant.

4. Others, such as the refractive dispersion with prisms, might be called 'shifts' though they add a lateral spatial dimension.

Spectral wavelength shift is often popularly called red or blue because red is the longer-wave end, and blue is the shorter end of the visible spectrum.

Red shift is therefore a shift toward longer wavelengths. When extreme, red shift can drive wavelengths well past the visible, into the infrared, millimeter, meter or longer wavelengths. Red shift occurs in all three mentioned above - Doppler, Gravitational, and Hubble Red. (Might be a good name for beer.)

Blue shift is a shift toward shorter wavelengths such as, when seen from visible light, the blue end of the rainbow spectrum. Blue shift occurs in velocity and gravitational shift only. Blue shift cannot be observed in Hubble Red Shift, because Hubble Red Shift depends on distance in space-time, and negative distances in the cosmological sense do not exist.

Generally, Hubble Red Shift is observed reaching much greater magnitude than either of velocity or gravitational shift. SyntheticET (talk) 20:41, 23 October 2008 (UTC)

Your 1, 2, and 3 are different aspects of the same thing, and we ought to explain that as much as we keep them distinct. 4 is different, but is never called redshift to my knowledge. -- BenRG (talk) 16:49, 28 February 2009 (UTC)

Different kinds of redshift

There's only one kind of redshift in general relativity. Cosmological redshift, gravitational redshift and special relativistic redshift are approximate formulas that work in certain spacetime geometries with high degrees of symmetry. They're very useful approximations, but their ontological status is the same as that of linearized gravity. Saying that there are two kinds of redshift, Doppler and cosmological, is the same as saying that there are two kinds of gravity, linear gravity and the nonlinear corrections. I'm mentioning this partly in reference to the image recently created and added by Brews ohare, which I copied on the right. I hate deleting images that people obviously spent time on, but I really think the article is better without this one. -- BenRG (talk) 16:40, 28 February 2009 (UTC)

Point well taken. It's one that's difficult to accept because so many people are convinced that the Doppler effect is responsible for the cosmological redshift when, in fact, it is strictly not a Doppler effect at all. Disambiguation can be taken too far, and I think that you rightly point out that this image may go a bit overboard. ScienceApologist (talk) 01:51, 1 March 2009 (UTC)

In response: (i) the image does not say there are two kinds of redshift, but that it illustrates two sources of redshift. (Gravitational redshift would make three sources). (ii) as indicated in the caption, this figure is very similar to one in a textbook; how misleading can it be?? (iii) in very many sources the distinction between Doppler and cosmological origins is made with exactly this example: the point is that in the cosmological case the stretch of wavelength occurs after the light leaves the source and so is obviously independent of the relative motion of the emitter and receiver. I believe these remarks strongly support retaining the figure. Brews ohare (talk) 22:58, 1 March 2009 (UTC)

On light-like spacetime intervals there is no "after the light leaves the source". There is only emission and observation. ScienceApologist (talk) 23:10, 1 March 2009 (UTC)

And in terms of the figure that means … ? See Harrison, a reputed figure in the field with many oft-cited publications. To quote: "Light leaves a galaxy, which is stationary in its local region of space, and is eventually received by observers who are stationary in their own local region of space. Between the galaxy and the observer, light travels through vast regions of expanding space. As a result, all wavelengths of the light are stretched by the expansion of space (see Figure 15.1). It is as simple as that." And here is a figure with a similar idea from a source different than that in the caption Jones et al. Brews ohare (talk) 23:44, 1 March 2009 (UTC)

This explanation is not quite right. The verbalization misses the point that integrating along a light-like geodesic does not only require the movement through vast amounts of space but also vast amounts of time. If light just traveled on space-like geodesics there would be possible observations that would have no redshift whatsoever. ScienceApologist (talk) 00:24, 2 March 2009 (UTC)

Normal thought process would expect that to travel from point A to point B would take time. Do you think all three figures are misleading? This one, Jones', and Theo Koupelis, Karl F. Kuhn (2007). In Quest of the Universe (5 ed.). Jones & Bartlett Publishers. p. 557. ISBN 0763743879.? Brews ohare (talk) 00:57, 2 March 2009 (UTC)

What I pointed out, however, is that the "normal thought processes" are misleading since it doesn't take any "time" at all since ds^2=0. It is a light-like geodesic, is all. That's neither "time" nor "space", in some sense. The three figures are perhaps needlessly complicated and are not equipped to handle some of the subtleties of these ideas. ScienceApologist (talk) 01:00, 2 March 2009 (UTC)

The Doppler shift diagram is beyond dispute, I'd guess? Every EM book in existence uses it. Brews ohare (talk) 01:06, 2 March 2009 (UTC)

We actually already have an image which illustrates this. The approaching/receding ball. ScienceApologist (talk) 01:08, 2 March 2009 (UTC)

Do you take issue with Harrison's description? Do you think the diagram is at variance with his description? Do you think that some comments about light-like space-time intervals or the ontological status of linearized gravity will make things clearer? Can you explain simply some unified viewpoint that makes Doppler shift, gravitational shift and cosmological shift all approximations of some universal formula expressing the same single physical fact? And would anyone care? Or, would they continue to use the simpler formulation as more in keeping with normal intuition? Brews ohare (talk) 00:11, 2 March 2009 (UTC)

I don't have easy answers to most of your questions. The figure itself seems to not do a very good job of explaining the situation, in my opinion, but I really don't care that much. The bigger problem is when people confuse explanations. Anything that gets people to understand better is great. Perhaps we should ask for a third opinion. ScienceApologist (talk) 00:24, 2 March 2009 (UTC)

The questions vary in complexity. For example, yes or no will do for the first two:

Do you take issue with Harrison's description?
Do you think the diagram is at variance with his description?

And, I expect the answer to this one is "no"?

Can you explain simply some unified viewpoint that makes Doppler shift, gravitational shift and cosmological shift all approximations of some universal formula expressing the same single physical fact? Brews ohare (talk) 01:03, 2 March 2009 (UTC)

- Yes.
- Not sure. The diagram has a weird "green shift" which I don't understand.
- To get a redshift, simply use the tt component of the metric at point A and divide it into the tt component of the metric at point B. The square root of this value is 1 + z. That's true no matter what the shift is. ScienceApologist (talk) 01:06, 2 March 2009 (UTC)

Hmmm.-I am not aware that the Doppler shift works this way as a metric related matter. Brews ohare (talk) 01:09, 2 March 2009 (UTC)

Yes, it works. It requires a transformation of coordinates from t to t', but it works. ScienceApologist (talk) 01:11, 2 March 2009 (UTC)

Can you provide a description available on-line? I'd like to learn a bit more. As for my "green shift", the idea was that the blue light stretching longer would become green before it became red. Brews ohare (talk) 01:15, 2 March 2009 (UTC)

Well, that's green shift is sorely confusing... I still am not sure I understand it since the blue waves appear to overlap with the green waves which overlap with the red waves. In any case, the derivation you request is essentially here with the full GR-metric notation left out because the only terms of relevance are the tt terms. ScienceApologist (talk) 01:25, 2 March 2009 (UTC)

This derivation assumes an emitter moving with velocity v and simply does a little coordinate algebra to find the wavelength change. That doesn't seem to me to be related to a model of cosmological expansion. Brews ohare (talk) 01:42, 2 March 2009 (UTC)

The coordinate algebra also is what is done to derive the cosmological redshift. It's the same derivation, just different assumptions about the metric. That's why 1+z=(1+z_pec)(1+z_H) since the components simply multiply when you tack on the additional assumptions. If you need more, I suggest looking at MTW. ScienceApologist (talk) 02:02, 2 March 2009 (UTC)

I assume this reference is to isbn 9780716703440? Is there no reference available on-line? Brews ohare (talk) 02:19, 2 March 2009 (UTC)

I revised the figure to take your overlap comments into account somewhat. Continuous gradation of color is a bit beyond me. Brews ohare (talk) 02:06, 2 March 2009 (UTC)

Brews ohare, you recently added to another article an excellent paper by Bunn and Hogg which explains this in detail, and a short diatribe by John Peacock which says the same thing. Harrison mentions curvature and expansion in the same breath as properties of spacetime but fails to notice the difference, which is that there's a curvature tensor but no expansion tensor. Expansion isn't a definable property of spacetime in general relativity. If I give you a region of spacetime with galaxy worldlines in it, there's no way to tell how much of their relative motion is due to Hubble expansion and how much is peculiar motion—and it doesn't matter, since you can treat it all as peculiar or all as Hubble and you'll get the same value for the redshift (and all other measurable quantities) either way. Harrison and the textbooks are wrong. It happens all the time in cosmology. Think of this as another equal-transit-time fallacy or taste map of the tongue. -- BenRG (talk) 02:28, 2 March 2009 (UTC)

Hi BenRG: Well have you the confidence and the energy to write an appropriate well-documented discussion? I've looked at a ton of texts on this subject and find them all over the map. Personally, your view that all velocities are velocities makes more sense to me than the expanding balloon idea where space expands between galaxies but not inside them. Brews ohare (talk) 02:54, 2 March 2009 (UTC)

In other news, I now understand what your image is going for and have to say that BenRG is right on the money with his critique. It falls into the traps warned about by Bunn & Hogg and Peacocke. The idea that the "stretching" of space is what somehow allows for the "stretching" of the wavelength of light is only true in a proximate sense. In the sense in which your drawing is made, it is actually incorrect: mixing two different perspectives -- one that relies on contiguous Minkowski arrangements and one that treats the scale factor multiplied by the radial coordinate as the difference between two reference frames. This is, in my mind, more misleading than it is informative, I'm sorry to say. ScienceApologist (talk) 14:24, 2 March 2009 (UTC)

I hear you. Here's my take on this - let me know your reaction. The various authors mentioned (Harrison, Jones et al., Kopellis & Kuhn) all use figures and a matching discussion that agrees with the figure we're discussing. That is, this figure is not worse than these sources, but you think these sources have prostituted the analysis to get an easy presentation.

There are dissenting voices outside this mainstream, for example, Whiting, Bunn&Hogg, Baryshev, and Peacock. I take it that you would agree with them?

So (i) are you and the dissenters right? See Francis et al. (ii) if you are, can the diagram be fixed to suit you? and (iii) if it can or if it cannot, can a suitable presentation be made? It would require more than a figure: it would require a convincing and documented exposition. It also would be necessary to point out the flaws in the very widely disseminated but unsatisfactory argument associated with the diagram.

In addition, the very widely used expanding balloon argument (also in the present Wiki article) in which space expands between galaxies but does not expand inside galaxies would have to be dissed. Brews ohare (talk) 17:37, 2 March 2009 (UTC)

Here is a discussion that might be a starting point: Hobson et al. Brews ohare (talk) 19:20, 2 March 2009 (UTC)

I'm not sure we actually need a diagram for this, but I'll mull these ideas over for a bit. In any case, this is good food for thought. ScienceApologist (talk) 19:23, 2 March 2009 (UTC)

Thanks for that link. It is a cautionary example of the kind of mess we can get into here. It appears that the right analogy to the math is not available right now. So maybe it's best to leave things in their present widely disseminated but misleading form until something better comes along? It's hard to believe that we are going to come up with a great analogy when many skilled and thoughtful types well versed in the theory cannot. Brews ohare (talk) 19:52, 2 March 2009 (UTC)

Here's a proposal: Leave the present discussion as it is, but add a "Mathematical analysis" section following Hobson et al. with the preamble that analogy is imperfect and subject to debate (see so-and-so) so next is a mathematical derivation of red shift that stems from GR and does not invoke any analogy. Brews ohare (talk) 20:03, 2 March 2009 (UTC)

Halton Arp

Why would this article benefit from a see also link to this one fringe astronomer? The other links are to related theories, which seems much more appropriate. If he has made some significant contribution to the field, let us just write about it like we do Doppler and Hubble. - 2/0 (formerly Eldereft) (cont.) 03:52, 3 May 2009 (UTC)

If it wasn't for the link I wouldn't have known about intrinsic redshift but now I do. Just giving other readers the same opportunity to learn.Landed little marsdon (talk) 13:00, 3 May 2009 (UTC)

Including some implausible hypotheses in the main article

A long-standing version of this article contained the statement "Alternative hypotheses are not generally considered plausible." with a footnote mentioning tired light and intrinsic redshift. A recent edit changed this sentence to "Alternative hypotheses and explanations for redshift such as tired light or intrinsic redshift are not generally considered plausible." I am reverting this sentence for two reasons. First, it provides undue weight to the implausible in an article that should remain focused on an observable phenomenon and what actually causes it. Second, it provides undue weight to two possible implausibilities when countless other incorrect hypotheses could be mentioned. A consensus among editors determined that the original method best served the reader. Flying Jazz (talk) 01:21, 22 May 2009 (UTC)

You have misunderstood undue weight. That these alternatives exist is not a minority view. It is a simple fact that is very reliably sourced. With their inclusion the article is far more informative than without.Landed little marsdon (talk) 07:31, 22 May 2009 (UTC)

Obviously, we disagree about applying undue weight in this particular instance. I would never claim that you misunderstand the entire concept. That would be uncivil. I would like to understand your logic about information. You claim that moving information from a footnote to the main article creates a "far more informative" article. If you move a couple pieces of fruit from the fridge to a fruit bowl, do you also claim to have far more fruit? Flying Jazz (talk) 13:19, 22 May 2009 (UTC)

Your own claims succumb to this argument far more than mine. That is, "informative" has an accessibility dimension to it that can be altered by rearrangement far more easily than the almost totally quantitative notion of weight. Thus, how does merely moving fruit out of the fridge increase its weight to an undue level. Re your point about civility, you seem to have had no qualms below about launching into a personal attack. Landed little marsdon (talk) 17:11, 22 May 2009 (UTC)

Could you list a few of those countless other hypotheses, especially ones with their own Wikipedia article? --Art Carlson (talk) 09:24, 22 May 2009 (UTC)

See one list of possible lists at Talk:Redshift/Archive 7#Attempting (again) to focus the discussion and bring sanity to the talk page and the ensuing discussion. In every complex area of science, there is a verifiable history of a large number of rejected hypotheses, so my view a few years ago was that neither tired light nor intrinsic redshift should be mentioned in this article--not even in a footnote. But the consensus was against me, and I'm neither an astronomer nor an edit warrior, so I believe tired light and intrinsic redshift were both mentioned in a footnote when the article became featured. What's changed since this article became featured? Is there any new importance that's been attributed to tired light and intrinsic redshift that justifies moving them from a footnote to the main article? To my (very limited) knowledge, there has been none. The only recent change is internal to Wikipedia: ScienceApologist has been banned. Does this mean that redshift mechanisms related to non-standard cosmologies may now be safely moved out of the featured-article-consensus footnote and into the main article? Well, without ScienceApologist here, my opinion is that there seems to be a POV-pushing edit warrior on one side of the issue but not the other. What do you think will happen to the article? Flying Jazz (talk) 13:19, 22 May 2009 (UTC)

It is not that easy to extract actual candidates from the discussion you linked. CREIL is mentioned several times, but CREIL redirects to Raman scattering, which does not even mention redshift. Also CREIL has had much less significance in the astronomical community than even tired light and intrinsic redshifts, so I think that would be in a different category. The Wolf effect at least has its own article, which is strongly oriented to astronomy, so that might fit better, although it is less significant historically. Ian Tresman notwithstanding, I don't know what else could be included in the list. ... But I didn't realize before that there was also a lengthy footnote. I think at least the footnote should stay (but tired light and intrinsic redshift should be wikilinked there). Given the footnote, I would have a weak preference for streamlining the text, i.e. not mentioning the specifics there. --Art Carlson (talk) 14:56, 22 May 2009 (UTC)

I prefer the mention in the article proper and a reduction of the footnote. That being said, I am not convinced by the current placement, and think that given the additional stuff mentioned by Jazz we should ago for a brief paragraph in the history section which lists but in no way advocates some of the alternative views. This way, the reader gets a much more comprehensive and accurate picture of the topic, as opposed to one which focuses on the currently accepted view alone. I guess this is the difference between a general encyclopedia entry and a scientific text book description.Landed little marsdon (talk) 17:22, 22 May 2009 (UTC)

The current sentence looks good to me

FWIW, I think it is a good idea to mention the two most important classes of alternative redshift theory in the main article, as is done now, with a sentence which leads to an informative footnote with links to "nonstandard cosmologies" article: "Alternative hypotheses and explanations for redshift such as tired light or intrinsic redshift are not generally considered plausible." I think this is a factual statement - these are not generally considered plausible.

I think a "See-also" section mentioning these would be good, but I don't feel like arguing strongly for it. "Tired light", "Intrinsic redshift" and "non-standard cosmologies" all have their own articles and are clearly important to the redshift question. This longer form of the sentence is a very minor burden in this suitably longish article, so I don't support reducing it to a shorter version which does not mention tired light and intrinsic redshift.

In the absence of an article on "alternative redshift theories", I guess the "non-standard cosmologies" is a good place to mention any such theories which are sufficiently notable. Redshift is absolutely central to cosmology, and since no-one has got out a tape measure and directly observed the distant objects receding, the current Doppler-based accepted theory should be regarded as a theory whose validity is not beyond question.

I feel that anyone who argues strongly against including mention of, and links to articles about "tired light" or "intrinsic redshift" is probably trying to protect readers from theories which this person is sure are untrue. Without reading the formal WP definition of neutral POV, I think that such an attitude and exclusion of mention is not a neutral POV. I am sure "intrinsic redshift" is untrue, but I think it is important that these theories be in WP articles and linked to from the main redshift article. There are multiple potential tired light theories, so just because the well known ones are easily falsified doesn't mean new ones won't be. (I don't accept that Sn1A observations or others absolutely prove expansion. There are prominent astrophycists who question the BBT, so any theory which is contrary to the BBT should not necessarily be excluded as lacking notability or as unworthy of mention in a science article.)

Science is a debate. To present it as a series of established facts is to completely misrepresent it - and also to strip away a lot of the excitement and interest which properly belongs with a question as momentous as the nature of the redshift of distant astonomical objects. I think WP should support readers who view science as a debate. So the article should make it easy for them to find information about parts of the debate which may be poorly regarded now, but nonetheless formed part of the history of the debate - and might perhaps be further developed and better regarded in the future. A few extra words, an extensive footnote, and two in-article links to other articles seems like a good way of doing this.

I don't support the view, as I understand it, that because there are apparently lots of non-Doppler redshift theories, and because we don't want to mention all of them (perhaps some are not considered "notable") that we should not mention any of them. (Ari Brynjolfsson's http://arxiv.org/abs/astro-ph/0401420 is apparently still considered not notable enough to include in WP. It is a tired light theory, which could, if notable enough, have its own section in the tired light article.) Mentioning the two most prominent classes of theories seems fine, and the current sentence uses "such as", so it is not an attempt at a complete list. (Mr) Robin Whittle (talk) 12:04, 23 May 2009 (UTC)

Thank you, Robin, for posting your views on the talk page rather than altering the article first without consensus as others have done. To learn more about your opinions, I hope you don't mind if I refer other editors to your web pages at http://astroneu.com/ and http://astroneu.com/plasma-redshift-1/ . If you'd prefer I not do this then feel free to remove this sentence and the previous one from my comments. Nobody to date has argued strongly for removing links to Tired Light and Intrinsic Redshift from the article footnote. Flying Jazz (talk) 12:53, 23 May 2009 (UTC)

That's fine to point people to my site, but it is rather long and I don't yet have an alternative theory redshift theory to present. To save folks time: I point out, with references to a paper by Steven Cranmer, that conventional magnetic explanations of the heating and acceleration of the solar corona and wind are inadequate - therefore we shouldn't rule out some as yet not recognised interaction between electromagnetic radiation and sparse plasma is causing this heating and acceleration. In that context, I argue we shouldn't rule out some as-yet unrecognised tired light redshift affect in the sparse plasma or the IGM and at a greater rate per Mpc in the more concentrated IGM which no-doubt is falling into black holes (including, most likely "quasars"). I feel confident I can explain the heating, but I have a long way to go before I can explain it in a form ready for publication. This heating theory is not on my site. I would expect the same process to work in the IGM, heating it probably to hundreds of millions of degrees. If that theory works out OK in the years to come, maybe it might be found that the same or a similar process redshifts the light.

You wrote: "Nobody to date has argued strongly for removing links to Tired Light and Intrinsic Redshift from the article footnote." There are no such links in the footnote - that is http://en.wikipedia.org/wiki/Redshift#cite_note-reboul-40 . "Tired light" and "intrinsic redshift" are mentioned, but there is no link to articles from those words.

I understand you or someone else suggested that the mention of "tired light" and "intrinsic redshift" with their links be removed from the sentence at the end of para 1 under the heading "Observations in astronomy".

I am disagreeing with that suggestion. I would be happy if the current sentence and the footnote it references remained as is. Robin Whittle (talk) 13:09, 23 May 2009 (UTC)

If the sentence were removed from the main article, the links would certainly be replaced in the footnote. The link to nonstandard cosmologies would remain in the footnote. Flying Jazz (talk) 13:41, 23 May 2009 (UTC)

7 extra words & Theories can be important even if almost everyone agrees they are wrong

I am posting this above Flying Jazz's summary to keep it prominent in the discussion.

Thanks Flying Jazz for this summary. You have correctly represented my position. I was not aware that the proposed changes would involve the links to the "tired light" and "intrinsic redshift" articles being moved to the footnote, which is sensible.

It seems we have a big discussion here about the inclusion of 7 words in an article which is at least 5,000 words already. So this can't be a discussion about conciseness, length, etc. My guess is that the motivation to exclude these words must be based on a notion that the theories they identify are so unimportant or at odds with "science" as to not be worthy of mention in this Wikipedia article, except in a footnote.

I guess that a position such as this would arise from a view of science which is entirely, or at least inordinately, focused on the supposed facts which science embodies in its theories: celebrating what is believed to be successful science, and actively shunning or deriding that which is believed to be either unsuccessful science, or pseudoscience - to the point where mention of such things in this article is either not allowed, or is at least relegated to a footnote.

If the only thing which mattered in science was the factual accuracy of the theories, and if in fact tired light and intrinsic redshift are truly wrong, then perhaps this position of working so hard to exclude them from the main body of an encyclopaedic article would be justified.

There are two problems with this. Firstly, we don't really know if they are wrong. Strictly speaking, "intrinsic redshift" hasn't been ruled out, since no-one has travelled to a redshifted galaxy and measured its light at close quarters with a spectrograph. I am sure the theory is incorrect, because I find it much easier to imagine some shift in wavelength due to Doppler or some new process in the IGM than whole galaxies of matter emitting at a different wavelength. The cosmologies based on intrinsic redshift (such as Halton Arp's) are arguably unscientific, since in explaining the light from AGNs and QSOs, AFAIK, they ignore the evidence that it results from black holes. (I read "Seeing Red".)

While tired light theories to date are not generally regarded as passing muster, it can't be ruled out that one may in the future. Since we can't explain the heating of the solar corona, we shouldn't rule out the possibility that there is something we don't yet understand about the interaction of light and sparse plasmas - and maybe that involves redshift. The coherence length of most or all of the signals we observe from distant galaxies is shorter than the likely interparticle spacing of the IGM. So as the wavefront couples to the particles, being slowed down by each one (a particle is like a cloud of gas with a refractive index above 1.0, but just a rather small cloud) it can be seen the IGM is an inhomogeneous medium for the signals we observe. So it would be unscientific to rule out the possibility of redshift due to interactions such as this, where the wavefronts of light are continually being slowed down by particles, speeding up again in the vacuum etc, coupling some of their momentum to and from the particles etc. Tired light theories would not be needed if the observed redshift matched exactly that from measured movement of the sources. However, so far, no-one has "proved" (a dangerous word in science) the universe is expanding - since no-one has physically measured the distant galaxies moving away.

But even if, in truth (which none of us can know for sure) both classes of redshift theory, and all others other than the conventional Doppler-based theory, are in fact completely wrong, that does not mean that mention of them should be excluded from - or unreasonably relegated to footnotes within - an encyclopaedic article.

Science is a process - a debate. People who want to know the accepted theories really should be interested in the tests they have been put to. Some of those tests include competition with other theories. The "tired light" and "intrinsic redshift" classes of theories are vitally important in the current standing of the Doppler-based theory of the cosmological redshift. I think all readers should be interested in the alternatives to the conventional theory. Even if many are not - being uninterested in the processes of science and only interested in its currently accepted explanations - I believe an encyclopaedic article should be written in a manner which illuminates the development of the currently accepted theory. This involves mention of the alternatives.

In other words, the scientific standing of the conventional Doppler-based theory of cosmological redshift depends in part on the existence of alternative theories, the fact that they are not widely accepted, and most importantly in the arguments about their validity which lead to most people rejecting them and supporting the Doppler-based theory.

I am arguing that 7 words: "such as tired light or intrinsic redshift" be devoted to mentioning the two most prominent classes of alternative theories, with links to their WP articles. These classes of theories are clearly notable, otherwise they wouldn't have articles. Robin Whittle (talk) 16:31, 23 May 2009 (UTC)

That, particularly the second part, pretty much sums up my take on things, and there is very little I would want to add. Perhaps this: we are writing an encyclopedia here and not a science textbook. As such we need to cover historical and other details not necessarily supportive or even that related to current scientific thinking in a way that a textbook would not. Think of this as the difference between an article called 'Redshift' and an article called 'Current scientific thinking on redshift'. The former will, if it is a good article, include the latter, but it will also contain other things besides. It is these other things that make the article comprehensive and it is these other things that I am concerned with here. Landed little marsdon (talk) 17:07, 23 May 2009 (UTC)

Thanks Landed little marsdon. A science textbook which failed to mention the development of theories, including alternative theories and why they were rejected, would be a very poor text indeed. By discussing the currently accepted results of the scientific process without their historical context, such a textbook would not assist people in thinking scientifically. By portraying science *as* these results, with the implication that these results are better than those obtained by other means (divinatation, faith, rolling dice etc.), and celebrating the triumph of science by way of the apparent superiority of these results, such a textbook would be promoting science without helping readers understand the scientific process.

Strictly speaking, nothing is ever proven in science. Observations are made, questions are asked and experiments are conducted. Theories are proposed, debated, modified, discarded and revived. Maybe one theory survives (in the minds of most who are debating it) all challenges. But you don't know what you don't know, and theories may have to be altered or abandoned. Light shows no evidence of travelling in an ether - oops, there goes Newtonian mechanics. DNA methylation changes as cells develop in the body and is handed on to future generations - oops . . . complete rewrite of genetics to include epigenetics. Many auto-immune diseases turn out to be due to humans evolving a naturally over-responding immune response due to everpresent parasitic infections, especially by helminthic worms . . . major revisions required to immunology. Continental drift . . .

I think there are scientific theories which have now been so thoroughly tested, and for which no-one is proposing alternatives, that we can pretty safely regard them as "fact". For instance the motion of the planets around the Sun and the existence of galaxies. However, since we can't explain the heating of the solar corona and since there are many difficulties with the Big Bang Theory, I think the Doppler interpretation of the cosmological redshift is best thought of as a scientific work in progress. Robin Whittle (talk) 02:12, 24 May 2009 (UTC)

Has anything in the astronomical or physics community/literature changed to justify a more prominent position for tired light and intrinsic redshift in this article? Robin, after scrolling up through the talk page, I believe you are simply repeating and rephrasing arguments you've made since your arrival on this talk page in late 2006. From Dec 29, 2006: "I think this page would be more complete if it mentioned some theories which challenge the conventional explanation." From Dec 30, 2006: "I don't think the matter is settled enough to forget that this is a debate." From Jan 1, 2007: "By ignoring the unconventional, textbooks and encyclopedias (which are relied upon by most non-specialists and establish new entrants' conceptual framework) lock in the prevailing paradigm and make most people think that the field is settled and beyond question." And most recently from May 23, 2009: "the article should make it easy for them to find information about parts of the debate." My view of the talk page archives is that in late 2006/early 2007, your opinions about what should be done with the article were expressed, duly considered by a significant number of editors here, and, ultimately, rejected by consensus. Please understand from my summary below that I am considering two ways to proceed: seeking more editors from the community would definitely be the way to go if there were something new to discuss with them and if there were focused, non-repetitive people involved in the discussion. Otherwise, I think bringing more editors here would just be wasting their time and protecting the consensus featured article would definitely be the way for me to go along with seeking help from some admin or whatever they're called if it continues to be reverted. Flying Jazz (talk) 16:30, 24 May 2009 (UTC)

Landed little marsdon, is that really your take on things? That only 7 words should be moved from the footnote to the article? If so, then why did you argue for adding "a brief paragraph in the history section"? Are you writing the paragraph that you would like to see added or have you decided on path 2a below? You have until tomorrow to decide what you actually want. Are you able to focus on anything and discuss that particular thing with other editors at Wikipedia? Or will you decide tomorrow to argue for something entirely different in order to continue to disrupt the article and disrupt Wikipedia again and again? Flying Jazz (talk) 16:41, 24 May 2009 (UTC)

Hi Flying Jazz, Please ignore whatever I wrote before yesterday. My preference is for the sentence to remain as it is, for at least the reason that "tired light" and "intrinsic redshift" are significant parts of the debate which resulted in the Doppler-based interpretation being widely accepted. These are notable theories about the topic, with their own articles. Devoting a few words in the body of the article to these classes of theory, with links to their article, seems a bare minimum an encyclopedic article should do in terms of enabling readers to understand the scientific debate. Those theories are scientific theories - they are not pseudoscience. They can and have been scientifically tested - and they have been rejected.

I will be interested to see if anyone takes up my challenge and argues why 7 words in a 5000+ word article is too much to devote to these rejected theories. However, I won't write any more. Robin Whittle (talk) 03:33, 25 May 2009 (UTC)

I think it is essential for anyone who would accept the footnote but reject the in-article links to address this point. I cannot even begin to understand how the footnote can be perfectly ok while the other is completely unacceptable.Landed little marsdon (talk) 14:44, 25 May 2009 (UTC)

Of course. I will address this point and Robin's post head-on. It has to do with ways of thought. Most people believe that their ways of thought are awfully good, that others think like they do, and that those who do not think like they do should change their mind. Robin has often stated that science is a debate. However, this is only half the story. This is the half of the story that advocates of fringe theories mention. Here is the other half. Science is a debate with consequences. The consequences are that the accepted ideas become prominent and the rejected ideas lose prominence. The rejected ideas never disappear entirely. They remain in the old literature for anyone to view and discuss. My way of thought is that one of the consequences when a hypothesis is rejected by the scientific community is that the idea should be mentioned less prominently in an encyclopedia article, if it is mentioned at all. I believe that's an awfully good way of thought. I believe most editors, admins, advocates, arbitrators, and others at Wikipedia would agree with me, but maybe I'm wrong. My only question at this point is who to disturb first if Landed little marsden reverts me again? Should I bother the people at Project: Astronomy for something that seems so obvious or should I go directly to the bureaucratic types? I suppose both would be best. Flying Jazz (talk) 15:55, 25 May 2009 (UTC)

Summary of Viewpoints about the prominence of Halton Arp, Intrinsic redshift, and Tired light and how to proceed from here

Please note that I have begun to refactor the talk page to place this summary and plan at the bottom. I will continue to do so until Monday May 25. My goal is to clarify the discourse to date for the benefit of new editors who arrive. If any editor does not want this to happen, feel free to remove this paragraph and return this section to its original chronological position.

Please let me know if I've misrepresented your recent opinions:

Art: has a weak preference for the long-standing, consensus featured article version where links to Halton Arp, Intrinsic Redshift, Tired Light were in a long footnote.
Flying Jazz: I have a weak preference for none of these topics being mentioned at all, but mentioning them in the long footnote is a close second and I concede to the long-standing, consensus featured article version.
Robin Whittle: prefers the new version where links to Intrinsic Redshift and Tired Light have been moved from the footnote to a sentence in the article itself. Would prefer a See Also list but does not feel like arguing strongly for it.
Landed little marsdon: Maybe wants Halton Arp in a See Also list (diff). Or perhaps wants Intrinsic Redshift along with several other items in a See Also list (diff). Maybe wants Intrinsic redshift in a See Also list with nothing else there (diff). Seems to want the links to Intrinsic redshift and Tired light in the main body of the text instead of in the footnote (diff). But most recently, in the talk page above, wants "The additional stuff mentioned by Jazz" here in a paragraph in the History section.

Here is my suggestion for how to proceed.

1) Please spend the next two days correcting any misinterpretations I may may have made in the above list.
2) Landed little marsdon, please spend the next two days deciding precisely what you would like to include in the article so we know your single, specific, exact, and focused proposal.

2a) If your proposal is only to maintain your most recent edit (diff) then write that down in the talk page and that is what we will discuss.
2b) If your proposal is to include an entire paragraph in the history section based on my comments here, please use the next two days to create that paragraph, place it here on the talk page, and we will also discuss that paragraph in addition to 2a.

3) Beginning on Monday, I will do one of the following:

3a) If Landed little marsdon is able to decide exactly what he/she wants by choosing path 2a or 2b, then something may occur that resembles an actual, focused disagreement among adults about a specific matter. In that case, I will post a notice at Wikipedia_talk:WikiProject_Astronomy asking for a larger community of editors to help us with the editing impasse.
3b) If Landed little marsdon is unable to decide exactly what he/she wants by choosing path 2a or 2b or if he/she pretends to choose a specific path and then avoids focusing on it later in the discourse, then I don't think a focused discussion among adults will be possible with this editor. I will simply stop engaging him or her, revert, and if my revert is reverted, I'll go and whine to some admin or arbitrator or whatever they're called. I've been on Wikipedia for four years and never done that before, but there's a first time for everything. Based on this user's recent history, if 3b occurs, I think the situation will be clear to any reasonable person who takes the time to investigate it. Flying Jazz (talk) 13:46, 23 May 2009 (UTC)

My view, which appears to be in line with the majority of editors who commented some years ago, is that that the article would be better if it contained a brief reference to tired light and intrinsic redshift. The exact wording is not something I feel needs to be decided on until the general point is agreed.Landed little marsdon (talk) 23:52, 24 May 2009 (UTC)

And to back up the idea that there was broad support in previous discussions for what I am saying, I would put forward this acknowledgement from scienceapologist (one of the main disputants from years ago) that tired light is highly notable, and this acknowledgement from flying jazz that his/her arguments against inclusion (the same arguments he/she is using again now) are not the best.[1] I quote:

'Well....OK. That's enough people who want it kept in for different reasons to convince me that maybe I was being too pedantic.'

Note also the admission that many people support inclusion. Landed little marsdon (talk) 10:57, 25 May 2009 (UTC)

Finally, perhaps you may be beginning to understand, Landed little marsdon! You are absolutely correct! That was the moment years ago that I recognized that a consensus of editors was for inclusion of a link to Tired Light, and yes, eventually, in the consensus featured article version, there it was, in a footnote, against what I thought was best. Thank you for tracking down that exact moment when, as a fair-minded editor in the Wikipedia community, I stopped arguing and stopped editing to remove it altogether because to do that would have been to disrupt the encyclopedia just as you have been doing. I am glad that you recognize a moment when I separated myself from the behavior of people like Iantresman, ScienceApologist, and yourself. I would never argue today for complete removal after that consensus had been reached. Flying Jazz (talk) 13:58, 25 May 2009 (UTC)

The type of mention of tired light being discussed in the above link, and being agreed upon by many editors then, and being objected to by you (then and now) using, as you admit, mere pedantry; was not a footnote reference as you are now falsely suggesting, but was in fact almost identical to the text I recently added. This can be seen clearly from this edit, made only a few days after the discussion from which the above quote was drawn. [2]. It is unclear why you are now resorting to the same discredited arguments in favour of exactly the same point when you have already conceded the point and the poor quality of your arguments many years ago.Landed little marsdon (talk) 14:35, 25 May 2009 (UTC)

There were many arguments about many topics during those months that led up to the article being featured. Most editors acting in good faith on a complex article will change their minds about the prominence of multiple things on multiple occasions. Eventually, after I was less active in developing the article, the consensus favored including a mention in a footnote. Please try to understand that when editors are actually collaborating to improve an article and bring it up to featured status, the Talk pages at Wikipedia become working social spaces rather than battlegrounds. It makes me giggle today that my statement from January 2006: "That's enough people who want it kept in for different reasons to convince me that maybe I was being too pedantic." is being used to discredit consensus opinions that were reached in my absence. Flying Jazz (talk) 16:27, 25 May 2009 (UTC)

Yeah, and it makes of giggle to see your idea of "adult discussion" is to completely ignore the statements you made above about the way forward, launch into a stream of personal attacks at every opportunity, and then just go ahead and implement your version even though the majority now, and previously,has always been against you. Landed little marsdon (talk) 16:36, 25 May 2009 (UTC)

If you would like to file a complaint about my behavior in recent days, there are administrators here who will read what you have to say and take both our words into account. If you believe the consensus would be with you, nothing is preventing you from posting a notice at Wikipedia_talk:WikiProject_Astronomy yourself to bring more knowledgeable editors here. Flying Jazz (talk) 17:08, 25 May 2009 (UTC)

Tired light

Tired light seems to me an obvious and undisputed part of the history of redshift. To exclude this topic from the history section leaves that section incomplete at best and revisionist at worst. Landed little marsdon (talk) 20:37, 25 May 2009 (UTC)

That's odd. Just yesterday you were arguing for something else. Hello to anyone joining us from the Astronomy Project. For any of you who have contributed to this article in the past, bringing it to featured status, thank you. I'd like to ask that you read the last couple sections of this talkpage before engaging in this discussion. Flying Jazz (talk) 20:56, 25 May 2009 (UTC)

The most recent edits placing mention of tired light and no other disregarded mechanisms into the main article are acceptable to me and resolve the edit warring and talk page conflict as far as I'm concerned. I am replacing the link to intrinsic redshift in the footnote, as promised to Robin above. Flying Jazz (talk) 10:10, 27 May 2009 (UTC)

What on Terra? Honestly I think that moving this interesting and historically relevant information into the footnote like that is unbecoming of a paperless encyclopedia, I think the information regarding these topics should remain visible to the reader. Unomi (talk) 10:32, 30 May 2009 (UTC)

Thanks Flying Jazz and Little landed marsdon. Robin Whittle (talk) 00:35, 20 June 2009 (UTC)

Seconding the suggestion of severe subtlety

These phenomena are so subtle that extra attention must be given to being very certain of the dimensions, relationships between observable quantities, and other concepts. Confusion is a part of every phenomenon - after all, c and h are the only constants in the wave and h is intrinsically uncertain in the way action is distributed among its dimensions.

Any study of red shift in light from very distant galaxies must begin with careful understanding. Is it shifted a linear, constant, nonlinear, exponential or some other mathematically definite way on the spectrographic record? That is, do specific short wavelengths such as known X-ray lines, shift the same amount as known microwave lines? If one were of high order propriety with the mathematics, what would be meant by "constant", "same amount" and so on? Is that a pure number multiplier, as, h*wavelength? Is it a particular wavelength, as "half a micron"? The dimensions of space, time, light waves, phase, frequency, wavenumber, energy, momentum, h and c seem to be well known but they are close to our imaginations when extremely far away, and the mathematics absolutely must start with very clear ideas of what they are.

Also, the term "tired light" is extremely destructive. It prejudicially condemns and excludes any inquiry into cases where wavelength might increase and momentum decrease, while their product, h, the action quantum, remains absolutely constant. By now, quantum mechanical causes of redshift are within the first ten sites listed on a Google search for the phrase "Hubble Red Shift ". SyntheticET (talk) 05:54, 24 April 2010 (UTC)184.78.143.168 (talk) 16:33, 13 February 2011 (UTC)

Redshift vs Blue shift

Interesting: this page is Redshift as opposed to Red shift, but Blueshift is called Blue shift. Is there a reason for this? -- 129.125.32.80 (talk) 11:52, 28 July 2009 (UTC)

It's an accident of history. Because in our universe red shifts are far and away more common than blue shifts and there is something of a trend in the English language toward compound words, redshift became a word while blue shift remained two different words. If the reverse had been true (blue shifts more common than red shifts) then I imagine the exact opposite would have happened. ScienceApologist (talk) 18:45, 30 July 2009 (UTC)

In the section entitled "Doppler Effect" the introduction to Transverse Redshift states, "Since the Lorentz factor is DEPENDENT ONLY ON THE MAGNITUDE OF THE VELOCITY, this causes the redshift associated with the relativistic correction to be INDEPENDENT OF THE ORIENTATION OF THE SOURCE MOVEMENT." This is absolutely completely totally WRONG!!! Check the Wikipedia writeup in section "Transverse Doppler Effect" under the topic "Relativistic Doppler Effect" to find out the truth. The truth is much more subtle than this incorrect assumption. Please fix it ASAP!!! Thank you. 98.212.132.146 (talk) 11:25, 12 December 2010 (UTC)

I think you are the one who is *ahem* misinformed. jps (talk) 17:07, 13 December 2010 (UTC)

Rewrite in lead

In the lead section, my basic thrust was replacing the OR, belated, and clumsy discussion that the term RS "might be confusing". That involved rewriting a couple later 'graphs, and IMO i have made portions of several other later 'graphs redundant, tho i had not the courage (well, recklessness) to rewrite them as well, for i reached the limit of my specialized knowledge. (E.g., Minkowski space is a term i recognize but have never studied under that name -- is there more to it than the Lorentz transformation and the ~~time-space displacement time-space interval~~ simultaneity metric?) I hope others better suited will follow up.
--Jerzy•t 23:44, 14 January 2010 (UTC)

Re the same edit, i rewrote by extending to
Conversely, a decrease in wavelength is called blue shift, and generally seen where the source has orbital motion toward the Earth.

That's not all that's worth saying. (There can be contracting universes, and i'm pretty sure when you go into a gravity well, everything else gets blue shifted, and even more fun, what's grav-blue-shifted for everyone else goes back to normal, eh?) But i'm pretty sure that's all that should be said in the lead. My gut says that even aside from the redundancies, there's too much already in it.
--Jerzy•t 00:07, 15 January 2010 (UTC)

Confused image and caption

A variety of possible recession velocity vs. redshift functions including the simple linear relation *v = cz*; a variety of possible shapes from theories of cosmological expansion related to general relativity; and a curve that does not permit speeds faster than light in accordance with special relativity. All curves are linear at low redshifts. See Davis and Lineweaver.<ref name=D&L>Tamara M. Davis, Charles H. Lineweaver (2000). "Superluminal Recessional Velocities". *ArXiv preprint*.</ref>

I have removed this image and caption because what it says is wrong and I don't see any way to edit it that would make it correct and informative. It indicates that general relativity is inconsistent with special relativity which, of course, it is not. The two curves on the graph with these contrasting labels make the content either wrong, or extremely confusing. If there is a correct point behind this, I urge the contributor to consider whether it can be expressed in some other way, or omitted. Eric Drexler (talk) 07:46, 21 January 2010 (UTC)

The image isn't the best, but it is strangely compelling to me. The SR vs. GR considerations come from simply considering whether you have a metric expansion (as in FLRW formulations) or whether you have relativistic Doppler (as in SR formulations). Weirdly enough, many astrophysicists I know who aren't familiar with detailed cosmology are not aware that these two treatments result in different solutions for "recessional velocity". But in point of fact the entire brown area is allowed for all types of FLRW universes with the red line only being our best understanding of how the universe we live in behaves. The "linear" relation is simply false where it deviates from the others. I kinda like the image because it is useful from a pedagogical standpoint, but it requires a bit more explaining than can be done in a simple caption, I think. No objection to its removal. ScienceApologist (talk) 18:35, 22 January 2010 (UTC)

I'm a bit tantalized; it sounds like an article could be written on a topic you're hinting at, & could be in "See also" (but probably not linked from the article's prose?) -- tho i have no idea of the title.
The "linear" curve surely takes too much undeserved attention from all other accompanying material, by leaving the reader asking how a curve got seemingly mislabeled "linear".
Humans are visual critters, looking first and being deterred when what hits them in the face looks like nonsense; don't label a 2c, 3c, etc. axis as "Velocity" for readers who've had it drummed into their heads that v>c is nonsense: how about "Recession velocity" or "Effective velocity" or at least some formulation like "Proper velocity + cosmological recession velocity.
In the same breath, don't put 0 (velocity) alone at the origin. Label it 0 to the left and 0.01 below, or even break the horiz axis with a full cycle of sawtooth-wave, highlighting the origin's proper position infinitely far to the left.
The distinction must also be made, for many of our readers, between the curves being the same below some unstated threshold and the curves approaching one another asymptotically as v decreases.
For many of us, the horizontal axis strongly insinuates the dependent variable; that has some appeal for experimentalists, but wouldn't most of us be aided by thinking of v as the independent, and thus plotting it increasing to the right?
I'm not sure whether to blame the plotted data, the labels within it, or the caption for

"linear" not being distinguished from the tenable theories
the insinuation that SR as a physical theory is tenable, other than as a special case w/in GR, and
the suggestion, via the seeming brown envelope, that there is a no-solutions realm between the SR curve and the edge of the envelope.

--Jerzy•t 10:17, 27 January 2010 (UTC)

In any case, i intentionally broke the ref w/ nowiki, in order to make the lk useful on this talk page for those interested.
--Jerzy•t 10:17, 27 January 2010 (UTC)

A few comments on your comments:

The only reason the "linear" relation is not linear is because this graph is semilog. I think that's an appropriate way to show this material, but I agree it can be shocking to the uninitiated.
While it is true that information, energy, and matter cannot travel in excess of the speed of light through space, "recessional velocity" can be due to other effects (namely the metric expansion of space) which can cause the object to have an "effective" velocity much large than the speed of light. In fact, you can see from image itself where the recessional velocity goes past the speed of light for our universe which defines a part of space which is "unreachable": in a sense another kind of cosmological horizon. Since recessional velocities very well can be in excess of the speed of light, there is nothing really wrong with having a graph that extends to 2c, 3c, etc. The only issue I see is that while the GR/SR cases are physical, the "linear" case is not. But we aren't plotting real data anyway.
The fact that the origin of the x-axis is not zero is, in my mind, inconsequential. Is there really a huge difference between a tiny fraction and zero?
In this case, redshift is the independent variable because what one interprets as the "recessional velocity" is model-dependent.
If you assume that the recessional velocity is due to a physical movement of the object as opposed to a metric expansion, then the correct graph is the "SR" graph.
There do indeed exist solutions between the brown envelope and the SR solution, but they require hybridization of movement and expansion of space.

Hope this leads you in the directions you're looking for.

ScienceApologist (talk) 19:45, 27 January 2010 (UTC)

As it is now, the article states "In particular, Doppler redshift is bound by special relativity; thus v > c is impossible while, in contrast, v > c is possible for cosmological redshift because the space which separates the objects (for example, a quasar from the Earth) can expand faster than the speed of light.[32]" This is false, as the diagram above shows. Though speeds are limited to v < c, redshift is NOT bound by special relativity. Unlimited redshifts are caused by the time-dilation effect. (98.212.79.206 (talk) 19:45, 27 July 2010 (UTC))

Replying to my own post. The whole paragraph is a bit confusing. Apparently, some of the "popular" literature uses the nonrelativistic Doppler equation, then comes to the conclusion that unlimited redshift is impossible because velocity is limited to v < c. Of course, this is easily shown to be false. However, the paragraph says the "Doppler shift is bound by Special Relativity." It might be more appropriate to say "some of the popular literature claims the Doppler shift is bound by Special Relativity." And then give reference to Chodorowski, if appropriate. (JDoolin (talk) 15:56, 29 July 2010 (UTC))

Fixed, I believe. ScienceApologist (talk) 21:24, 4 August 2010 (UTC)

Quasars

Why is nothing said about quasars? I understand that quasars are an exception to the rule as their light is held up quite a bit by gravity until it leaves the quasar, giving it a huge red-shift. I also heard of half a quasar that had a huge redshift, and the other half had a big blue shift! Arlen22 (talk) 13:52, 11 June 2010 (UTC)

Quasars are mentioned in the article. I'm not sure why you think that they aren't. ScienceApologist (talk) 15:12, 4 August 2010 (UTC)

line element

I notice that this page refers to ds as line element whereas at special relativity it is the "square" quantity dx² that is referred to as "line element". It would be helpful to sort out the standard terminology. From the mathematical viewpoint, it is preferable to identify line element, element of length, and ds. Tkuvho (talk) 08:26, 4 August 2010 (UTC)

it should be the differential spacetime interval, I think. Good catch. ScienceApologist (talk) 15:13, 4 August 2010 (UTC)

Doppler effect works great in Aether

This is why I hate modern Physics. Relativity states that a photon is a photon whatever speed the emitter or receiver is traveling at. Why would there be a change in the wavelength because the source of the light is going at speed X in direction Y? And what happened to the lost energy from a lower wavelength photon, wait don't tell me, let me guess, someone arbitrarily assigned the energy to magically appear somewhere else.98.165.15.98 (talk) 15:47, 25 November 2010 (UTC)

Hubble finds a new contender for galaxy distance record

The information about the highest redshifts seems to have gone out of date on the 26th of January 2011 (today at time of writing.) The official ESA/NASA Hubble Space Telescope website reports the discovery of a new (old) galaxy with a redshift of about 10. The light from this galaxy traveled for about 13.2 billion years. Since this is obviously already a good article I wasn't sure how to go about editing it, especially in terms of making a properly formatted citation, as while I'm familiar with various formats I've never used Wikipedia's editing interface and was unsure how to get them to work out. Hopefully a more experienced contributor will see this and proceed to make the necessary edit. The report I'm talking about may be found here as a web page: http://www.spacetelescope.org/news/heic1103/ Or here as a PDF: http://www.spacetelescope.org/static/archives/releases/pdf/heic1103.pdf 41.199.32.84 (talk) 19:18, 26 January 2011 (UTC)

While this is likely a z = 10 galaxy, its redshift was not directly measured. 128.59.169.46 (talk) 19:24, 21 June 2011 (UTC)

"Two different sources of redshift" figure label

"The cosmological expansion panels are a concatenation of local inertial frames spanning the space between the various locally stationary objects." The way this is written, it means that no space is left out between the objects. In what sense are the local inertial frames concatenated? In the same sense that the chair across the room from me and the chair I'm sitting on are concatenated? There is no reason that this drawing could not apply to my chairs (thankfully it doesn't, or at least not in a noticeable way). Might it be better to say that "the cosmological expansion/contraction panels represent changes to objects that appear stationery to local observers while the space between them is changing."? 0¹⁸ (talk) 02:39, 14 August 2011 (UTC)

The issues are pretty subtle. What makes a "local inertial frame" in cosmological terms is the metric, and there is no expansion on scales that are smaller than cosmologically relevant. This is because the determination of the metric locally is made by whether or not objects are gravitationally bound. The fact that Andromeda is hurtling towards us literally means that space between us and Andromeda is not expanding. This is why this point is so important. Now, as soon as you enter a regime of cosmological relevance space is expanding. This occurs at different scales depending on the local density. For us, it's just beyond the distance to Andromeda. The question as to whether the "space" itself is expanding is a bit academic and, in fact, the general consensus of theorists is that this is something of a misnomer (read this, for example). What instead we have is a property of the metric called the time-dependent scale factor which yields recessional velocities, redshifts, and changing densities. Conceptually, one can get a pretty good handle on how this behavior works by proposing that the "space between objects" is changing, but, in fact, it's not the "space between" but rather the metric that is changing which is defined to arbitrary precision. It's just that the scale factor is only relevant on cosmological scales. So is the wording okay? It's hard to say, but I'm inclined to opine that your proposed wording may have a bit more of a misconception to it than the current wording, even though the current wording leaves something to be desired. 69.86.225.27 (talk) 03:42, 16 August 2011 (UTC)

No. "concatenation of local inertial frames spanning the space between" is blatherskite, your explanation does not change that. How about, "the cosmological expansion/contraction panels represent changes to objects that appear stationery to local observers while the metric of distance between them is changing." 0¹⁸ (talk) 04:34, 16 August 2011 (UTC)

On consideration of your proposal, I now think that the image is really problematic. I suggest it be removed entirely as it doesn't seem very useful and may, in fact, be entirely misleading. I think the point it's trying to make is that, "For an isotropic source of light, the observed redshift by distant observers in a cosmological scenario is isotropic while for the Doppler scenario there are, in general observed redshifts and blueshifts depending on which way and how quickly the object is traveling." That should be the caption and the rest should be excised. Or get rid of the entire image. 69.86.225.27 (talk) 12:26, 16 August 2011 (UTC)

What is the middle drawing on about? Is that supposed to be cosmological contraction? Is there such a thing?(talk) 14:34, 16 August 2011 (UTC)

I think the middle is the situation before the bottom panel. The blue light is shifted to red. In theory, if the universe were contracting we would see cosmological contraction and blueshifts. But we don't live in such a universe. It's obvious that this image is confusing. Let's get rid of it. 69.86.225.27 (talk) 04:42, 17 August 2011 (UTC)

Okay, but if we hacked out the middle panel, they might it be a good figure? 0¹⁸ (talk) 13:34, 17 August 2011 (UTC)

Possibly, though to what end I'm not sure. 69.86.225.27 (talk) 23:57, 17 August 2011 (UTC)

I don't get much of the article you linked to but, "To second order, it is exactly correct to think of the cosmological redshift as a combination of doppler and gravitational redshifts." suggests to me that expansion might be a third order (or higher) effect. Does it obey some known finite power law? 0¹⁸ (talk) 03:03, 18 August 2011 (UTC)

To first order, the cosmological redshift is the Galilean Doppler shift. To second order it is the combination of the special relativistic doppler shift and the gravitational redshift. This can be proved by expanding the solution of the Freidmann Equations for the inverse of the scale factor. 69.86.225.27 (talk) 02:43, 19 August 2011 (UTC)

And beyond that? 0¹⁸ (talk) 15:37, 19 August 2011 (UTC)

The third-order terms would include aspects of the metric which are proportional to r^3. These would be found primarily in the full solution, but I don't really have the physical intuition to know what the secular effect might be. There is a similar analysis that can be done for post-post-newtonian approximations around a spinning black hole, but there, if I recall correctly, the third-order terms had to do with frame-dragging and lensing neither of which are going to happen in FRW solutions because of the symmetries invoked to create the metric in the first place. It may be that these effects have no name and are just a part of the cosmology without analog to more prosaic geometries. 69.86.225.27 (talk) 06:50, 20 August 2011 (UTC)

Okay, I should have guessed that. Anyways, I think my questions has been answered with satisfactory clarity for the purposes of this article. Thanks. 0¹⁸ (talk) 19:16, 20 August 2011 (UTC)

Photograph

I plead complete and utter ignorance on this subject - but can redshift be photographed, and if so is it possible to incorporate an image of redshift actually occurring into the article? I suspect not as it already looks thorough but I thought it was worth asking. Thanks Yeanold Viskersenn 03:47, 29 December 2006 (UTC)

To "see" a redshift, the object would have to be traveling faster than any macroscopic object that exists here on Earth has ever traveled with respect to any other object. --ScienceApologist 04:11, 29 December 2006 (UTC)

Would it be possible to find two galaxies, matched for their physical parameters (number of stars, age, ellipticity, what-the-heck-do-I-know) and viewing angle, but one at low redshift and one at high redshift? Once the images are adjusted for size and brightness, it should be possible to see the difference in color in a true color image (I think). --Art Carlson 10:51, 29 December 2006 (UTC)

The best we can probably hope for is looking at HUDF objects. Those things look like red dots and the galaxies in their own frames are probably very blue starburst galaxies. --ScienceApologist 12:46, 29 December 2006 (UTC)

Interesting idea, and a question to embaress astronomers like me who can't tell you off the top of their heads if galaxy properties vary so much that redshift comparisons that are visually obvious are possible! Sdedeo (tips) 11:09, 29 December 2006 (UTC)

New high quality data is available at GOODS: The Great Observatories Origins Deep Survey. Follow the link Spectroscopy Master Catalog . In the table List of existing spectroscopic surveys in the CDFS with publicly available data, in the REDSHIFTS column to the right find a small number (to keep your first download brief) and select the Author's name link in the REFERENCE column. Click SEND PDF to have the document downloaded. SyntheticET (talk) 16:53, 13 February 2011 (UTC)SyntheticET (talk) 17:30, 13 February 2011 (UTC)

There are photographs of spectra, such as [3]. You can see the different redshifts of the same absorption feature. — Preceding unsigned comment added by 163.1.247.167 (talk) 13:05, 18 September 2012 (UTC)

frequency versus wavelength

Odd that there is an argument over this. This is correct. A change of variables has to be done using the identity:

{\frac {{\text{d}}f}{{\text{d}}\lambda }}=-{\frac {f}{\lambda }}

which is derived from taking the derivative of the frequency x wavelength = speed equation. This is essentially a result of frequency being a property of a covariant transformation while wavelength is a property of a contravariant transformation. The same confusion leads to, for example, the bizarre consequence for Wein's Law where the peak frequency of a blackbody spectrum is not just the speed of light divided by the peak wavelength of the same spectrum.

Be amazed.

69.86.225.27 (talk) 04:20, 27 November 2011 (UTC)

Close, but no cigar. The fact is that redshift is an observable. Sure, if you go by the theory on the Doppler shift article then you'll get the equations you think are correct. But the fact is that the observed redshift is defined simply through a substitution of variables because the physical interpretation of the Doppler Effect causing redshift is only correct up to the point that you integrate along the null geodesic. Instantaneously the difference between the two formulae vanishes, but the two formulae diverge at high redshift due to the fact that there has to be a frame-transformation. If you want redshift to mean v/c subject to the assumptions found in the Doppler shift article, then you have to execute the change of variables as outlined above. But if you want redshift to mean "the fractional difference in observed versus emitted spectra" then you go with a simple substitution. 128.59.171.194 (talk) 23:47, 28 November 2011 (UTC)

Strike all that. What is written above is more-or-less total nonsense. There is no sense in doing any of these machinations at all. The redshift-frequency equation is defined correctly now and has been made consistent with the Doppler effect article. Thus sayeth mathematical consistency! 128.59.171.194 (talk) 01:49, 29 November 2011 (UTC)

Other causes of redshift effect

This sentence states "There exist other physical processes that can lead to a shift in the frequency of electromagnetic radiation, including scattering and optical effects" Does scattering cause shifts in frequency? That is not my understanding of scattering. Scattering has a prism-like effect, with higher (bluer) frequencies being attenuated first. What arrives at the observer after passing through a scattering agent has less blue light in it. This is not a shift of frequency that could be measured with spectroscope. It is a change in the relative brightness of composite frequencies. If there are no objections, I wish to revise this sentence. AngleWyrm (talk) 22:36, 5 January 2012 (UTC)

As far as I can see, scattering refers to elastic scattering of photons off individual particles such as electrons (see Compton scattering). Such a process will result in a transfer of momentum, and for example where a cold cloud of particles is stationary relative to the observer, this transfer of momentum will result in a transfer of energy from a photon being scattered to the scattering particle. This will result in a reddening of a specific wavelength (a genuine shift in frequency), and not only the separation of wavelengths to which you refer. For clouds at higher temperatures this effect should remain, albeit with more complicated results, and it is to this effect that I think the article is referring. It would thus be inappropriate to modify the article in the way that you suggest. — Quondum^t_c 04:09, 6 January 2012 (UTC)

Alternative explanations besides cosmological expansion?

The article claims the distantly observed red shift is due to cosmological expansion of space. Since it says that, I think it could be greatly improved by mentioning (or linking) alternative explanations, the arguments against them, and an argument why no other plausible alternatives can be found. (Tired light? Time passing at a different rate?) SEppley (talk) 13:04, 26 October 2011 (UTC)

Already discussed to death in the archives. The short answer is that the "alternative explanations" are already covered in the article sufficient to their exposure in the mainstream literature which is what we care about in writing an accurate encyclopedia article. Tired light is mentioned in this article to the extent that it is considered viable by the best sources about what "redshift" is. 69.86.225.27 (talk) 03:37, 27 November 2011 (UTC)

Argument against mainstream viewpoint:

Quasars do not display 'time dilation' ( Pending problems in QSOs, 2009, Corredoira :"Time dilation, which is observed in supernovae, should also be observed in QSOs, increasing the periods of variability with the distance, but it is not observed in QSOs against expectations (Hawkins 2010)". This fact argues against the existence of a relevant cosmological speed and thus also against the usual cosmological interpretation of the redshift. This caveat should be mentioned in this article, IMO. Heldervelez (talk) 04:17, 11 July 2012 (UTC)

Since quasars do not have any uniform object-to-object variability timescale, and there are good reasons to believe that they should intrinsically exhibit different timescales depending on mass, accretion rate, etc., there is no strong reason to expect that one could detect time dilation using quasars. Lopez-Corredoira's work is exceedingly FRINGE and doesn't belong here. - Parejkoj (talk) 14:59, 11 July 2012 (UTC)

An alternative explanation of the cosmological redshift::

The interpretation of redshift assumes implicitly that atoms have an invariant size through time. Because there is no law or physical principle that supports or denies it, it is possible to interpret the redshift as evidence that the atoms may have been larger in the past.

That atoms can vary thru time was formally demonstrated in this paper: A self-similar model of the Universe unveils the nature of dark energy (vixra) (not peer reviewed). As the above paragraph in italics is a strong argument and it is obviously correct I think that some wording like that could be posted in the main article. I understand the politics of WP and I'm not asking to link to the paper because it is 'Original Research'. But the 2 or 3 sentences in italics is simply 'common shared knowledge' and I dont think that anyone can claim that it is incorrect. Also, no one can claim for 'sources' of laws that no one can find in the corpus of physics nor in the WP. All the measures we take are based in atomic properties rendering the atom the ultimate reference of itself. I would like to know if there is any objection to the inclusion of that content.

Heldervelez (talk) 04:17, 11 July 2012 (UTC) I've corrected corpsus of physics by corpus of physics because corpsus is the latin word for 'cadaver (i.e. dead body)' and it was an involuntary error. Heldervelez (talk) 11:59, 11 July 2012 (UTC) (again I'm trying to correct that word Heldervelez (talk) 12:49, 11 July 2012 (UTC) )

vixra is not a reliable source. - Parejkoj (talk) 14:59, 11 July 2012 (UTC)

Derivation of cosmological redshift

The derivation hinges on the fact that the scale factor $a$ has been moved to the $dt$ integral on the LHS. If it had been left with $dr$ on the RHS (as it appears in the expression for the metric) then the "result" (treating $a$ as a constant) would indicate no redshift. It should be made more explicit that (in this model) $a$ is a function of $t$ but is not a function of $r$ ; this is indeed an important physics point, not only mathematical. The stretching of the light happens "wherever it has got to" at the same rate, and that is why the redshift depends in such a simple way only on its "age". — Preceding unsigned comment added by 163.1.247.167 (talk) 12:41, 18 September 2012 (UTC)

It says that *

a

is the time-dependent cosmic scale factor in the derivation explicitly. — Preceding unsigned comment added by 131.142.52.96 (talk) 15:53, 25 September 2012 (UTC)