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frequency: ν or f

f for frequency was changed in ν. That may be more common in physics books, but f is also in use. IMO, f is much clearer for non-specialists, while ν is easily confused with v for velocity. Harald88 01:16, 5 August 2006 (UTC)

Agreed, as long as we mention that f = frequency. --Iantresman 10:03, 6 August 2006 (UTC)

Edits to the headings

I've changed History to a level 1 heading (I think this was left as a level 2 heading from a previous edit) and I've also removed the word redshift from some of the headings where it's obvious that we're talking about redshift (eg. History of redshift -> History). I'm leaving a note here since there is one change I'm not so sure about: Quantifying and interpreting redshift: z -> Quantification and interpretation: z. If I've done wrong, please feel free to revert. Cheers, darkliight 14:17, 18 August 2006 (UTC)

Cosmological redshift

The cosmological redshift is not a Doppler effect, but is caused by the stretching of space. It is analagous to the Dopler effect. The redshift caused by motion through space (eg of stars) is a Doppler effect (not just analogous). See Gravitation, by Misner, Thorne & Wheeler.

Sorry I am new to this game and forgot to sign the above. Charlie T, 19 August 06

This is correct, but that's exactly what the article says at this time. --ScienceApologist 09:11, 19 August 2006 (UTC)

Doppler redshift of source

The text notes that "A single photon propagated through a vacuum can redshift in several distinct ways". Doesn't a moving source appears to be a different mechanism since it requires a physical source in addition to said photon, and the redshift occur BEFORE said photon leaves the source surface and enters the hypothetical vacuum? --Iantresman 11:47, 28 August 2006 (UTC)

According to Galilean relativity, there is no "source" nor "observer" needed because you cannot distinguish between a moving source and a moving observer, therefore the source and observer are just place-holders in the equations and are not relevant to the mechanism. The definition of a reference frame abstraction is simply a change in perspective -- something which can occur while the photon is sailing through the vacuum of spacetime. --ScienceApologist 11:59, 28 August 2006 (UTC)
If you can't distinguish between a moving source or observer, then how can you infer a redshift? Perhaps there is a confusion in the text between "mechanism" and "transformation"; the former causes the latter. In practice, a moving sources CAUSES a redshift? --Iantresman 13:29, 28 August 2006 (UTC)
There is physically no way to determine whether a source is moving or whether an observer is moving. Trying to distinguish between the two is artificial to physics -- a weak form of the equivalence principle. The transformation is the mechanism. --ScienceApologist 13:40, 29 August 2006 (UTC)
  • It's just that I thought that the article tells us that we can calculate the radial velocity of an object from its redshift.
  • It occurs to me that "mechanism" might be the wrong word. The transformations are surely descriptions. The mechanism for the Doppler shift is surely the velocity of a source or observer; the mechanism of the cosmological redshift is surely the expansion of the universe. The transformation describe the effects? --Iantresman 22:18, 29 August 2006 (UTC)
This seems to be a matter of semantics rather than substance. I had an earlier discussion with User:Serjeant about the difference between cause and description and we never really resolved the issue. Mechanisms and descriptions to me are basically the same since science ultimately only answers the questions of "how" and not "why". --ScienceApologist 00:24, 30 August 2006 (UTC)
  • To me, and I should think most other readers, a mechanism should related to a real world analogy. The siren on an ambulance does not change tone due to the mechanism of "frame transformation"; it changes tone because the truck is moving. Likewise, the optical redshift of stars is CAUSED by the mechanism of stars moving. Mathematically and conceptually, this can also be described as a frame transformation. --Iantresman 08:30, 30 August 2006 (UTC)
You say "poh-TAY-toh", I say "poh-TAH-toh". The siren on an ambulance does change tone due to the mechanism of a frame transformation. In fact, such a physical description is more accurate that relying on the nebulous "truck is moving" observation. The CAUSE is the fact that the siren is in a different frame of reference from the observer. A stationary siren with a moving observer would therefore result in the same phenomenon. --ScienceApologist 13:28, 30 August 2006 (UTC)

Redshift transformations

I can find no refernces that describe redshift mechanisms:

  1. as a group of only three (or four), that are...
  2. due to Galilean, Lorentz, and general relativistic transformations, and...
  3. applying only to single photons in a vacuum.

Sure I can find references that describe a redshift as a certain transformation, but nothing which groups all three/four redshifts with all three transformations, and to single photons in a vacuum. This leads me to suggest that:

  1. transformations are not synonymous with mechanisms
  2. transformations are not necessarily the only type of mechanism
  3. that this summary of mechanism is highly selective and contrived.
  4. "single photons in a vacuum" is not a necessarirequirement of redshift mechanism.

--Iantresman 10:05, 30 August 2006 (UTC)

I would suggest you read some of the introductory physics and astronomy texts suggested. By the way, the "single photon" application is an idealization, not a requirement. You can read previous discussions about this. --ScienceApologist 13:29, 30 August 2006 (UTC)

I've tried various textbooks and journals, and can find no citation that describes redshift as it is described in the article, and summarised above. --Iantresman 14:13, 31 August 2006 (UTC)

Look at, for example, Peebles, Principles of Physical Cosmology Chapter 5, where the first three are discussed in detail. Although, he doesn't explicitly call the first a galilean transformation -- since that derivation can be found in almost any introductory physics text book. Salsb 14:51, 31 August 2006 (UTC)
OK, I've had a look in the book and could find:
  • Nothing on Redshift mechanisms, (so there does not appear to be a "link" to transformations)
  • Nothing on photons in a vacuum
  • One mention of photons moving in free space, in relation to tired light (p.225)
So while I have no problems with the transformations per se, there does not appear to be a suggestion that these are mechanisms, nor any of the other points that I summarised above. --Iantresman 15:30, 31 August 2006 (UTC)
I am afraid you haven't read carefully then. The chapter, pages 94-99, specifically discusses doppler effects, and shows you specifically the transformations required to obtain the first two in detail, although you have to do some math to transform them precisely into the form in the table. Furthermore, the discussion and mathematics is specifically in the context of particles in vacuum. Salsb 15:42, 31 August 2006 (UTC)
  • OK, I have read through them, and am quite happy with the Doppler redshift being described as a Galilean transformation. But I can find nothing which describes the transformation as being the mechanism.
  • It seems to me that motion of the source or observer is the mechanism; the transformation is the description.
  • Indeed, all I find elsewhere are references that suggest that the "Doppler effect" is the mechanism, . And the Doppler effect is described as being caused by the motion of the source of observer.
  • Again, I can find no references that suggest that the redshift mechanisms are due to any transformation --Iantresman 16:02, 31 August 2006 (UTC)

Mechanistic descriptions are what physics does. There is no distinction in physics between mechanism and description because, to paraphrase Feynmann, physics asks "How?" and not "Why?" For example, the Doppler Effect is described fully by the Galilean transformation which means that the two are synonymous for waveforms. --ScienceApologist 16:10, 31 August 2006 (UTC)

  • So why do ALL the citation that I have found, tell me that one of the redshift mechanisms is due to the Doppler effect, and NO-ONE has been able to find a citation supporting the description that one of the redshift mechanisms is due to a Galilean transformation, or any other transformation? Again, I am not disputing that the Doppler redshift is described by a Galilean transformation.
  • Even if the description is technically correct, why should the Wiki article on Redshift be the ONLY ARTICLE ON THE PLANET, to describe redshift mechanisms in this way? --Iantresman 17:54, 31 August 2006 (UTC)
We've been through this already. Take it up with dispute resolution if you want. Protracted circular conversations like this should be avoided. --ScienceApologist 17:58, 31 August 2006 (UTC)
It's not circular. I've asked for a citation supporting the description, and no-one can provide one. The only conclusion is that the article statement is not verifiable. --Iantresman 18:47, 31 August 2006 (UTC)
Valid point - it's not hard to understand why it's hard to find such an unphysical description in the literature. Most literature distinguishes between mathematics (transformations) and physics (Doppler effect). Harald88 21:52, 31 August 2006 (UTC)
Untrue. Go ahead and support your claim with a citation that says that transformations are distinct from the Doppler Effect: or more precisely that the mathematical description of such a phenomena is "unphysical". The citations are provided, the naysayers have no evidence to back-up their claims. This discussion is over until the disputants can make a coherent, verifiable case for themselves. --ScienceApologist 14:22, 1 September 2006 (UTC)
Please don't put things on their heads. What is criticized on this Talk page without support from literature has to go. Simple as that. Harald88 22:38, 1 September 2006 (UTC)
  • The "disputants" could not be clearer; The statements in the article are not backed up by ANY citations. It is yourself that has no evidence. To DEMOMSTRATE that this is incorrect, all you have to do is provide a veriable quotation that describes redshift mechanisms in terms of transformation.
  • I will happily provide some verifiable quotes which unamibiguious describe redshift mechanisms in verifiable terms. --Iantresman 14:48, 1 September 2006 (UTC)
"This discussion is over." What kind of language is that? Just who the f*** do you think you are? Jon 10:11, 4 September 2006 (UTC)

Verifiable quotes on "redshift mechanisms"

No citations have been provide describing redshift mechanisms as frame transformations; this can be remedied by providing a single attributable quote containing the words "redshift", "mechanism" and "transformation" and any of "Galilean", "Lorentz", or "general relativistic".

I offer the following quotes describing redshift mechanisms, as described in the literature (emphases mine):

  • "Modern physics knows two experimentally verified mechanisms which produce redshifts that are independent of wavelength... the Doppler effect ... the Gravitational redshift. Besides these empirical and well understood redshift mechanisms, there is the theoretical phenomenon associated with the expansion of space. Thus three redshift mechanisms act in nature." -- Discovery of Cosmic Fractals] (2002) by Yurij Baryshev, Pekka Teerikorpi
  • "For historical reasons, small redshifts are often quoted in velocity units: the radial velocity required to produce the observed shift strictly from the Doppler mechanism due to relative motions." -- "The Road to Galaxy Formation" (2002) by William C Keel
  • "Attempts to interpret the red shift by a gravitational mechanism ... efforts have been made to interpret the red shift by a Doppler mechanism", The Red Shift: A Different Mechanism (1972) Urbanovich, S. I.

--Iantresman 16:26, 1 September 2006 (UTC)

note for InvictaHOG

About all the fact tags you lefd thruout, don't the links fulfil the need for citations? Or, why must they be in the same page? -lysdexia 20:54, 23 September 2006 (UTC)

No. Otherwise we would not have a referencing system. A person who wants to verify a statement should be directed to either the page of a book or a scientific paper with that conclusion. A link is not sufficient. This may be basic physics knowledge, but most people do not have basic physics knowledge. I'm not sure I understand your second question about the same page. InvictaHOG 21:05, 23 September 2006 (UTC)
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