Thus spake "John (Liberty) Bell"
Oh No wrote:

Thus spake "John (Liberty) Bell"
Oh No wrote:

Thus spake Joseph Lazio

JB John (Liberty) Bell wrote:
I think I've posted previously a reference to a paper that claimed
that Type II supernovae are difficult to detect beyond z ~ 0.5. The
most distant Type Ia supernova is about 1.7, IIRC.

Yes, that's right. SN1997ff is at z=3D1.755. In the Riess gold set the=
re
are only nine useful data points above z=3D1. Current surveys like the
Supernova Legacy Survey aren't even looking above about z=3D1, because=
of
measurement problems and risk of statistical bias in the data. We have
to wait for SNAP which should turn up hundreds, or even thousands of SN
at red shifts up to 2.

The reference (ApJ, 649, 563-569, 2006) provided by

(http://groups.google.com/group/sci.a..._frm/thread/1a
777a781e67a3a2/#)
indicates that there is no conclusive _observational_ evidence of q
becoming positive at z0.5.

The ref. provided by Rob was ApJ, 649, 563-569, 2006. I found the paper
by checking the contents of the most recent issues of the Journal. This
paper is less than 2 months old.
Authors: Charles Shapiro and Michael S. Turner . The ref. given by The
Astrophysical Journal at the top of the paper is 649:563-569, 2006
=A9 2006Date: Oct. 1 2006

This paper takes the non-standard step of dispensing with the Friedmann
equation. Not something I would be inclined to do, since the Friedmann
equation is itself based on well established physics. The most I would
consider reasonable is to allow the cosmological constant Lambda to vary
in time. This is done in a somewhat arcane group of theories often
called "quintescence". Of course if one does take a step like this then
one is no longer working within the context of a mainstream GR
cosmology, and obviously that opens up the possibility that q is not
determined at all times by the current data. However, there is an
immediate problem that, in this case, the amount of data is so little
that it is very difficult to come to any physics conclusions at all.
Mostly these theories are being tested by looking for supernova at z1,
because that is where we are best able to collect data with which to
test them. Other projects are underway, but I believe they are mostly in
early design and build stage. As I understand, at the moment there is no
evidence for varying Lambda. If you are talking about such theories
outside of standard cosmology, you should make your context plain.

Although the paper says that there is only week *observational* evidence
of past deceleration, such deceleration is a feature of a standard GR
cosmology, and it concludes that "none of the kinematic models studied
here have revealed robust features about cosmic acceleration that differ
from LambdaCDM or wCDM. Moreover, none of the kinematic models fit the
data significantly better".

I'll let you search arxiv yourself for galaxies around z=3D10. I don't
think there are many found so far.

I am only aware of 1, which was subsequently discredited. That is why I
asked you for your references.

I had said that the data was too thin to use. It does not altogether
surprise me if the observation has been discredited. I gather the
moderator gave references earlier in the thread.


Regards

--
Charles Francis
substitute charles for NotI to email