Cosmic acceleration rediscovered

The following post was banned from sci.astro.research, sans notice (as
usual).
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"Phillip Helbig---remove CLOTHES to reply"

wrote in message ...
In article , "Lars Wahlin"
writes:

A few years ago data from the Ia Supernova Cosmology Project found that
Hubble's law is not linear but changes in a nonlinear fashion at large
distances, i.e. The universe is accelerating.

This is just plain wrong. Hubble's Law says that recession velocity is
proportional to distance.

The "Hubble's law" to which you are referring is a theoretical construct.
Hubble's data connects distance with redshift -- not with recession
velocity.

This is actually quite trivial, since this is
the only relation which allows a homogeneous and isotropic universe to
remain so.

Your assumption has nothing to do with the discussion of the Hubble
relation. And it may have nothing to do with the real universe.

However, both the distance and velocity are not observable.

The distance is observable. The redshift is observable. The assumption
that velocity is the only contribution to redshift is pure theory (not
observable). Just like the last time this was discussed on this N.G.

http://www.google.com/groups?selm=10....supernews.com

Hubble's actual discovery was the linear apparent-magnitude--redshift
relation.

Carl Wirtz' discovery was the empirical redshift-distance relation in 1924
(pre Cepheid variable identification).

Hubble gave us the distance - redshift relation. He used Cepheid variable
stars to set the distance. And it is apparently linear for galaxies with
resolveable Cepheids. Again, just like it was discussed before in this N.G.
http://www.google.com/groups?selm=mt...tar.bris.ac.uk

FOR LOW REDSHIFT, one can use the former as a measure of
distance and the latter as a measure of velocity. However, this
relation is almost always observed whatever the cosmological parameters,
and is just a consequence of the fact that "things are linear to first
order".

In other words, "Hubble's Law" is by definition linear.

Argument-by-definition is not valid in the scientific method.

That you, and other theorists, like to assume that the distance-redshift
relationship is purely linear does not constrain the real universe. The
effect you are looking at may not be linear ... it may simply be the first
part of an exponential function.

What you mean is that a departure from this linearity is observed at
higher redshift, which indicates an expanding universe.

It only indicates an expanding universe if your assumption is true. Which
is not a given.

Well, this was actually
suggested long ago by Karachentsev .Commun. Buyrakan Obs. 39 96. (1967),
Ozernoy,Zh. Eksper. Teor. Fiz (Letters) 10, 394 (=JETP Letters 10 251),
(1969), de Vacouleurs, Publ. Astron. Pacific 83, 113 (1971) and
verified theoretically by myself (Wahlin, Astrophysics and space Science
74, 157 (1981)).

As Bill Press said in 1995, someone knows the value of the Hubble
constant to 1%---we just don't know who that person is.

Totally irrelevant.

I am not aware
of ANY observation-based arguments for an accelerating universe before
the 1990s which still stand up today. Sure, some people made some
observations and drew some conclusions. Maybe by chance the conclusions
were even correct. But it was just luck. Make a thousand predictions,
and one might be right.

Like your conclusion that the distance - redshift relation might be linear?
Unfortunately, this assumption will no longer 'stand up today.' The
supernovae data blew it away.

--
greywolf42
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