# Talk:Hubble's law

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## Acceleration reference suggestion

Recent high red shift distance determinations show a departure from Hubble's law that has been interpreted as indicating an accelerated cosmic expansion.<ref| S. Perlmutter, " Supernovae, Dark Energy, and the Accelerating Universe", Physics Today, April 2003, pp 53-60 [supernova.lbl.gov/PhysicsTodayArticle.pdf] |/ref> (HCPotter (talk) 09:39, 1 January 2012 (UTC))

## Photon expansion

Although the cosmic red shift is interpreted as a Doppler effect associated with remote light source recession relative to a local observer, actual spatial separation increase has not been verified. For photons with volume proportional to wavelength cubed, cosmic red shift is associated with photon expansion during the journey to the present from deep time and photons could be likened to bubbles rising in an effervescent liquid.Effervescence Such expansion could be mistaken for a Doppler red shift. If combined with the standard photon electromagnetic field <ref| H. C. Potter, "Metanalysis validates comprehensive two part photon", Apeiron 18:3(2011)254-69. [1] |/ref>, added per photon dimming would reduce determined stellar distances, decelerating cosmic expansion.(HCPotter (talk) 09:34, 15 January 2012 (UTC))

## Merger from Dimensionless Hubble parameter

I went ahead and merged the content from Dimensionless Hubble parameter into the article (with minimal alteration to italicise h and H0). I probably didn't follow the exact merging procedure, but it seemed to me like a reasonably clear-cut case, since even Hubble's constant itself doesn't have an article. I put the content under Interpretation, as it seemed too long to put in the intro. Hopefully, that's a good place for it. -Anagogist (talk) 22:55, 29 February 2012 (UTC)

This is really not 'dimensionless', since it really amounts to the measure of $H_0$ in parsec.seconds/dm. It's like saying that measures in millimetres (on engineering diagrams, numbers without measures are m/m measures) are also dimensionless numbers.

The hubble constant is $H_0$ = $h$ dm/pc.s. The hubble unit is then "dm / pc.s " or (100 km/s)/(MPc). Wendy.krieger (talk) 07:24, 5 June 2012 (UTC)

## File:Edwin Hubble.jpg Nominated for Deletion

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## Cumulative Phase-Alteration of Galactic-Light Passing Through Cosmic-Microwave-Background: Possible New Mechanism for the Cosmological-Redshift

Possible New Mechanism for the Cosmological-Redshift: In the volume-III of Progress in Physics, July 2012, possible new mechanism for the cosmological-redshift has been proposed by Hasmukh K. Tank. This mechanism can account for a large percentage of the redshift; reducing the requirement of 'dark-energy', may be, to the observable 5% mass of baryonic-matter. [Ref. Tank H. K. "Cumulative-Phase-Alteration of Galactic-Light Passing Through the Cosmic-Microwave-Background: A New Mechanism for Some Observed Spectral-Shifts" Progress in Physics, Vol 3, July 2012, pp 39-42] — Preceding unsigned comment added by 122.102.126.92 (talk) 17:26, 8 August 2012 (UTC)

Perhaps in a few years, when there are wp:secondary sources for this. - DVdm (talk) 18:06, 8 August 2012 (UTC)

## Not Lemaître's Law

If you search Google Lemaître's law, you won't find any citations except on Wikipedia of references to that name. Yes, there is evidence recently that Lemaître may have actually first derived the law, but that doesn't mean the law's name suddenly changes. As far as I can tell, there is no real effort in the scientific community to change the name; as a result, the name is as it stands right now: Hubble's law. I removed the "or Lemaître's law" portion a while ago with a detailed rationale in the comment, but that change appears to have been reverted by someone who failed to provide any reason for doing so. As Wikipedia is not the place to start such a movement to change the name of a scientific law, I will (again) remove that portion. ALK (Talk) 04:19, 20 December 2012 (UTC)

I agree. The bibliographic credit for discovery has been discussed in the recent 2-3 years, as is indicated by the references in this article, and Hubble's role is less god-like than it was earlier. But there's little movement to change the name "Hubble's Law" to "Lemaitre's Law" (or the Slipher-Wirtz-...-Lemaitre-Hubble Law). In the absence of a reliable source, I'm reverting to your (ALK)'s correction. Boud (talk) 22:21, 30 October 2013 (UTC)

## Spherically-Expanding-Wave-Front of Light Viewed as Gated-Plane-Wave, to Understand the Cosmological Red-Shift

"A spherically-expanding-wave can be viewed as a plane-wave passing through a gate, of slit-width Δ d = 2 c t . As the wave-front progresses, the equivalent-width of the gate-function goes on increasing. This is equivalent to multiplying in space-domain, a sinusoidal-wave with a gate-function of width Δ d = 2 c t ; and when we Fourier-transform it, we get a spectrum which goes on shifting toward lower-wave-number-side, as the wave-front expands. This attempt leads to an insight that it is the wave-front which expands, and not necessarily the ‘space’! And the ‘cosmological-red-shift’ may be simply due to this ‘propagation-property’ of light." From the abstract of a manuscript by: Hasmukh K. Tank, who had previously proposed a view that a spherically-expanding-electromagnetic-wave-of-light can be veiwed as a wave within a wave-guide-cavity, which goes on increasing with the wave-front of the spherically-expanding-wave. 121.246.200.77 (talk) 10:48, 4 March 2013 (UTC)

## Doppler shift → relative velocity

April 3, 2013 the very first sentence in this article states: "Hubble's law is the name for the astronomical observation in physical cosmology that: (1) all objects observed in deep space (intergalactic space) are found to have a Doppler shift observable relative velocity to Earth, and to each other...". I challenge the assertion that we have OBSERVED their Doppler shift from anyplace other than Earth. It is a simple statement of fact, which I am confident is just plain wrong. It is disappointing that the authors can not distinguish between measurements and theory. Most high school students can, when taught the difference.173.189.76.217 (talk) 12:53, 3 April 2013 (UTC)

• You might have mistaken what is meant by relative velocity. From earth we can observe two light sources in the same area of the sky that have different red shifts compared to each other (an observable "fact"). We infer that the source with the greater red shift is moving away faster (and thus is farther away) (according to theory). 75.208.245.67 (talk) 06:54, 2 July 2013 (UTC)
In Galilean relativity or Minkowski spacetime, velocity in general is a vector, so talking about "to each other" is ambiguous to the reader. In reality, in general relativity velocity is a local property of a worldline - you can't arbitrarily shift it somewhere else without saying (at least implicitly) in what way you shift a four-vector from one spacetime location to another. For the lead of this article, IMHO stating that the speeds are approximately proportional to the distance is reasonable as an approximate explanation. Boud (talk) 02:37, 31 October 2013 (UTC)

## Derivation of the Hubble parameter - Needs Reliable Sources

Can someone who knows what they are talking about please check if this edit is correct? Thank you in advance. Richard75 (talk) 17:00, 5 May 2013 (UTC)

Yes, help citing Reliable Sources seems needed for the Hubble's law article - trying to validate derivations seems to be quite a challenge esp since there seems to be few Reliable Sources cited - are some of the derivations and/or uncited statements Original Research? - added several relevant templates ({ {Citation needed |reason=reliable source needed to validate derivation |date=May 2013}}) to the article - in any case - Enjoy! :) Drbogdan (talk) 20:20, 5 May 2013 (UTC)
• No, they are not. This section derivations are quite standard. See most courses on Cosmology, eg. Cambridge Part III[1] — Preceding unsigned comment added by 128.232.251.85 (talk) 14:33, 5 April 2014 (UTC)

## proportionality regime

From a hidden comment in the article: I though this was applicable to anywhere from a few 10 Mpc to the edge of the observable universe.

I've added refs to the main SNe type Ia papers - Fig 1 of Perlmutter et al and Fig 4 of Riess et al have log-log redshift-luminosity diagrams. Divide the vertical axis (m-M) by 5 to get a log10 axis scale in comoving radial distance (to match the log10 z scale), provided that we ignore the extra (1+z)^2 effect in the luminostiy distance. On a log-log scale, the non-linearity is not so obvious, but it's easy to see that at z about 1 or so the dependence on the curvature parameters (Omega_m, Omega_Lambda) is significant.
Depending on what is interpreted as "approximately", going to z=0.3 or z=1 could be considered approximately linear. But then there's the problem of when to inform the reader that z is not proportional to the Minkowski spacetime Doppler interpretation of a cosmological redshift as a speed (which is a valid interpretation after parallel transporting the velocity four-vector along a null geodesic from the emitter to the observer). Leaving these aspects until later/deeper articles is possible by limiting the "approximately valid" scale to a few 100 Mpc, maybe 1 Gpc.
The image at File:CosmoDistanceMeasures_z_to_1e4.png also makes it clear that above a redshift of about 0.1, the various notions of distance that can be useful in cosmology start diverging. Boud (talk) 02:54, 31 October 2013 (UTC)
There's also a linear distance vs log10 redshift diagram at File:Distance compared to z.png - you can invert this mentally by imagining a (positive) exponential that fits the left part of the main curve - it's clear that this has to fail somewhere no higher than z about 1. Or you could download the cosmdist GPL'd commandline tool (or use its C or fortran library) and make an actual calculation... Boud (talk) 03:13, 31 October 2013 (UTC)
And finally, even easier: a linear-linear plot: File:CosmoDistanceMeasures z to onehalf.png. Divergence of various distance measures is clear starting from about z=0.1, depending on which sort of distance you choose. This gives zc approx 30000km/s, divide by H0 approx 70km/s/Mpc, and we get 400 Mpc. So "a few 100 Mpc" is reasonable. Boud (talk) 03:30, 31 October 2013 (UTC)

## Doppler shift interpretation

Recently an IP made some changes to the Doppler interpretation section [2], and I revert them on grounds of accuracy. However, they gave a link to arXiv:0808.1081, which contains very convincing arguments that things can be interpreted as a Doppler shift. I think the section should be rewritten with the arguments made by arXiv:0808.1081 in mind. 14:27, 18 December 2013 (UTC)

## Hubble Diagram - in initial explanation why is it not considered to show velocity again time

I visited this page to find why Hubble diagram is not interpreted as expansion velocities being greater the further back in time you look (because light has taken longer to travel from more distant galaxies). The verbal description didn't answer this fairly obvious issue of interpretation. Is it possible to add a little more explanation about how the time aspect of these observations is incorporated in calculation of the Hubble constant, or why it is generally not mentioned in the verbal descriptions aimed at non-cosmologists. Dr S Richardson (talk) 21:37, 3 March 2014 (UTC)

## Proposed Changes to "Observed values" table

I believe the dates in the first column should be changed to YYYY-MMM-DD format, ie. 2001-May, 2009-Feb, 2013-Mar-21. At first I thought 2001-05 meant that the data was from the period 2001 to 2005, rather than May 2001. I believe my proposal will improve clarity. Tdf4638 (talk) 22:01, 27 March 2014 (UTC)

## Graphic

File:Hubble-constant-vers2.png should be removed as it contains outdated data. Correct (up to date) information is more important to the reader than pretty pictures. 00:08, 10 April 2014 (UTC)

I would argue that it is not "outdated," but "historical" in nature. The entire section the image is found in pertains to the narrowing down of H0 and the different values researchers have found for it over the years. If anything should be changed it should be the description, so that it is more obvious that there is historical context. In the meantime, I'll start work on an updated graphic. Primefac (talk) 08:50, 10 April 2014 (UTC)