Re: Galaxies without dark matter halos?

Phillip Helbig---remove CLOTHES to reply <[EMAIL PROTECTED]>
wrote in message news:[EMAIL PROTECTED]
> In article <[EMAIL PROTECTED]>, greywolf42
> <[EMAIL PROTECTED]> writes:
>
>>> The point is that the non-linearity is NOT completely arbitrary, but is
>>> easily explained by an idea which has been around for decades.
>>
>> 'Dark energy' has not been around for decades.  It was not even floated
>> until the observations of supernovae disproved the linear Hubble
>>assumption.
>
> First mistake: there never was a "linear Hubble assumption".  Go back
> and read cosmology papers from the 1920s and 1930s.  The relation
> between apparent magnitude (of "standard candles") and redshift is
> linear at small redshifts only.  ("To first order, the relationship is
> linear".  Duh.  No big deal.)

> Admittedly, there is some confusion
> since there is an EXACT linear relation---at all redshifts---between
> velocity and distance,  but both the velocity and the distance involved
> are not observable quantities.

Could you please expand upon this difference, a bit?  I thought the redshift
vs. distance relation *was* the Hubble constant.  It is true that this is
usually *interpreted* by theory (and plotted by texts) as velocity vs.
distance -- but the experimental Hubble constant is redshift vs. distance.
The latter now determined by Cepheid variables in the nearby galaxies.

> However, since you mention the
> observations of supernovae, I assume you are referring to the relation
> between the observables apparent magnitude and redshift.

Yep.

> To clear up
> any remaining confusion:
>
> @ARTICLE      {EHarrison93a,
>                AUTHOR       = "Edward R. Harrison",
>                TITLE        = "The Redshift-Distance and Velocity-Distance
>                                Laws",
>                JOURNAL      = APJ,
>                YEAR         = "1993",
>                  VOLUME       = "403",
>                  NUMBER       = "1",
>                  PAGES        = "28",
>                  MONTH        = jan,}


> Second mistake: "dark energy" is simply the cosmological constant, by
> any other name.  (I don't like the name, simply because it confuses
> things.)  Some people see "dark energy" to be more general: different
> equation of state, time-dependent.

Then the 'cosmological constant' is not the same as what is discussed as
'dark energy.'  All poodles are dogs, but not all dogs are poodles.

> But there have been speculations
> about time-dependent cosmological "constants" for a long time as well.

True.  But dark energy is not necessarily a cosmological constant.

> (Unlike the Hubble constant, where "constant" means "constant everywhere
> in space at a given cosmic time",

Actually, the Hubble constant is a local empirical constant -- not
theoretical.  You may postulate a theory wherein the 'Hubble constant' is
global, and one wherein it changes with time.  But this was not the original
'Hubble constant.'

> the cosmological constant has more the
> meaning of "constant of integration".  The capital-Lambda (i.e. not
> normalised with the Hubble constant) is, in the simplest theories,
> indeed constant with time.)
>
> You make it sound like people were surprised by the non-linearity of the
> Hubble diagram for SN Ia!  Far from it!

There were many who *were* suprised by all reports.  Standard cosmologists,
for example.  If they had not been surprised, the name "dark energy" would
never have been coined.  Apparently, no deviation had been measured -- hence
it was not 'necessary' to the theory, and it fell out of favor.  It took
time to be resurrected into 'standard' cosmology.

> What was surprising was a) the
> technical achievement of gathering the observations

That was indeed a surprise.  I found the effort and process quite
exceptional.

> and b) the confirmation by an independent group.

Confirmation rarely surprises me -- one the methodology is known.

>> The m-z diagram for supernovae could as easily be explained by the
>> modified QM theory of JP Vigier.  Which really *has* been around
>> for decades. The m-z curve is in fact a curve of the type predicted
>> by Vigier's theory.
>
> Quantitative reference please.

Vigier had no quantification, just like Einstein had no quantification for
the cosmological constant.  Vigier had a QM constant -- similar in type to
the also-unquantified cosmological constant.

>>>> No need to distort my position with a strawman argument.  I simply note
>>>> that the "amount" and 'characteristics' of "dark energy" are backfit to
>>>> the observed m-z diagram.
>
> If I read off a number from a scale, is my weight "just" a back-fit?

It is, if you built the scale by using "you" as a standard weight.  This is
what was done for 'dark energy' from the m-z diagram.

>>>> Equations of state are theoretical constructs.  The observation is
>>>> simply that the "Hubble constant," isn't constant.
>>>
>>> You are displaying extreme lack of knowledge here.  The term "constant"
>>> in "Hubble constant" means that, at a given time, it is constant
>>> everywhere in the universe.
>>
>> The Hubble constant was defined in the 1920's to mean the relation
>> between the distance of a galaxy (containing a resolvable Cepheid
>> variable) and the redshift of the light from the galaxy.  There is --
>> and was -- no additional theoretical baggage about being constant
>> 'at a given time'.
>
> Wrong.  Even Hubble (who didn't call it the "Hubble constant") noted
> that he might be observing "the de Sitter effect", i.e. something which
> had been predicted theoretically earlier---and of course it was clear
> that this is a linear approximation at low redshifts.

Your view is consistent with the modern historical view.  As part of
teaching introductory Astronomy, I have often played a Nova video that
solemnly intones that the observations of Hubble showed what the mind of
Einstein had conceived.  History, however, differs significantly from this
pleasant myth.

While *a* constant was first deveoped in 1917 by Einstein, this constant was
explicitly to *prevent* change in his theoretical  STATIC relativistic
cosmology.  Einstein's relativistic cosmology was purely static until
1932 -- despite Friedmann's 1922 attempt to introduce a non-static metric.
(Einstein commented in the same journal that Friedmann's dynamic solution
was "incompatible with the field equations.")*  DeSitter was (at least
during the 1920's) strongly anti-relativistic cosmology.  Hence Hubble's
mention of a possible "DeSitter effect" may be his interpretation of a
theoretical prediction -- but certainly not one of relativistic cosmology's.

Carl Wirtz first published the empirical redshift-distance relation in 1924
(pre Cepheid variable identification).  Lemaitre's publication of the
'expanding universe' theory came in 1927, and was based partly on Wirtz'
empirical work. Hubble's version of the redshift relation was not published
until 1929 (after Cephied variable identification made Wirtz' relationship
more certain).  Eddington was the first relativistic cosmologist to
acknowledge the possibility of the dynamic universe AFTER seeing Hubble's
1929 work -- in 1930 (* p14).  "Eddington, rather shamefacedly, showed (his
assistant, G.C. McVittie) a letter from Lemaitre which reminded Eddington of
the solution of the problem which Lemaitre had already given.  Eddington
confessed that, though he had seen Lemaitre's paper in 1927, he had
completely forgotten about it until that moment." The term 'cosmical
constant' was (I belive) first coined by Eddington in his next book "The
Expanding Universe" in 1933.

*See "The Invented Universe, The Einstein-DeSitter Controversy (1916-1917)
and the Rise of Relativistic Cosmology" Kerszberg, 1989.

> Read papers by
> Sandage from the 40's and 50's where cosmology is described as a "search
> for two numbers", namely H and q.  The deceleration parameter q IS the
> deviation from the linear relation (i.e. the second-order parameter).

Papers from the 40s and 50s don't address the original finding of the
redshift-distance constant -- regardless of the name used for the constant.

greywolf42
ubi dubium ibi libertas