Speaking of Statistical Significance!

Le 10/06/2015 08:29, Phillip Helbig (undress to reply) a écrit :
Would you speak of "mounting evidence"? No. You would
probably say "one tentative result is not enough to convince me".

There are now *two* lines of evidence, as I told you in my previous post.

1) The article mentioned by Mr Oldershaw in this thread

2) The discovery that there are two groups of super novae populations
that differ by color (Mentioned in the thread "Dark energy doesn't
exist?" started on Apr 13th.

Yes, dark energy is not "proved wrong". But we are going into that
direction.

On Wednesday, June 10, 2015 at 2:30:18 AM UTC-4, Phillip Helbig (undress to reply) wrote:

The situation now is that essentially all observations support the
concordance model, then one observation looks to be a bit less secure.
Yet you tout this as indicating "dark energy doesn't exist" or whatever.

The universe is what it is, regardless of what anyone believes it to be
or wants it to be. The only thing which is important is a proper
interpretation of observations. ALL observations.

Would you agree that Paul Steinhardt, who is no slouch when it comes
to cosmology, would assess the observational support/conflict
situation for the LCDM model quite differently than you?

RLO
Fractal Cosmology

[Mod. note: reformatted -- mjh]

On Thursday, June 11, 2015 at 2:27:49 AM UTC-4, Robert L. Oldershaw wrote:

Would you agree that Paul Steinhardt, who is no slouch when it comes
to cosmology, would assess the observational support/conflict
situation for the LCDM model quite differently than you?

I suspect that Paul Steinhardt is a strong advocate for the basic LCDM mode=
l as described in the Wikipedia article ( http://en.wikipedia.org/wiki/Lamb=
da-CDM_model ). The universe is 13.8 billion years old and flat (zero cu=
rvature), and consists of ~70% dark energy (Lambda), ~26% cold dark matter =
(CDM) and 4% baryonic matter. Many of its properties, such its large-sc=
ale structure, can be predicted from analysis of the power spectrum of the =
cosmic microwave background.

Where Steinhardt disagrees with most of the cosmology community is in his r=
ejection of *inflation*
(http://physics.princeton.edu/~steinh/0411036.pdf ) which is supposed to ha=
ve occurred 10^(-32) seconds after the initial singularity. As Matt Str=
assler noted in his fine blog post
( http://profmattstrassler.com/2014/03...ig-bang-theor=
y-are-reliable/ ) we have very little direct data concerning this very earl=
y time, now that the BICEP2 data has been shown to have been affected by fo=
reground contamination. However, beginning with the period of nucleosy=
nthesis, the standard cosmological model should be considered very reliable=
, with multiple successful predictions.

--Wayne

In article ,
"Robert L. Oldershaw" writes:
http://arxiv.org/abs/1506.01354
"Marginal evidence for cosmological acceleration from Type Ia supernovae"

If you insist on a flat geometry, for which there is quite a bit of
evidence, the statistical significance goes up.

The preprint solves for B magnitudes, which after color and stretch
corrections have a dispersion of 0.10 magnitude. The intrinsic
dispersion goes down at longer wavelengths, and I'd expect, say, R
magnitudes would produce smaller error bars and therefore higher
significance. If this is taken into account in the preprint, it
isn't obvious to me.

Not related to the conclusion, the first words of the Abstract are
very strange. The authors write 'The "standard" model of cosmology
is founded on the basis that the expansion rate of the universe is
accelerating at present....' I'd say instead the standard model
(basically the Friedman equation) _contains adjustable parameters_
for the acceleration and its rate of change with time; nothing in the
model requires those to be non-zero. Observational tests show that
the acceleration is positive and its time variation (in comoving
units) smaller than can be measured.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

[[Mod. note -- Please limit your text to fit within 80 columns,
preferably around 70, so that readers don't have to scroll horizontally
to read each line. I have manually fixed up some, but not all, of the
garbled line-wrapping encodings in this article. -- jt]]

On Friday, June 12, 2015 at 12:42:46 PM UTC-4, wlandsman wrote:
On Thursday, June 11, 2015 at 2:27:49 AM UTC-4, Robert L. Oldershaw wrote:
=20
=20
Where Steinhardt disagrees with most of the cosmology community is in his r=3D
ejection of *inflation*
(http://physics.princeton.edu/~steinh/0411036.pdf ) which is supposed to ha=3D
ve occurred 10^(-32) seconds after the initial singularity. As Matt Str=3D
assler noted in his fine blog post
( http://profmattstrassler.com/2014/03...-bang-theor=3D
y-are-reliable/ ) we have very little direct data concerning this very earl=3D
y time, now that the BICEP2 data has been shown to have been affected by fo=3D
reground contamination. However, beginning with the period of nucleosy=3D
nthesis, the standard cosmological model should be considered very reliable=3D
, with multiple successful predictions.
=20

Also, Pavel Kroupa offers a radically different assessment of the
status of the LCDM model and offers a comprehensive list of
observational problems for the standard cosmological model. His
advocacy for MOND theories provides the motivation for this assessment,
but the problems he identifies can and should be viewed independently.

RLO
"It's a fractal world"

In article , jacobnavia
writes:

Would you speak of "mounting evidence"? No. You would
probably say "one tentative result is not enough to convince me".

There are now *two* lines of evidence, as I told you in my previous post.

1) The article mentioned by Mr Oldershaw in this thread

I've been away (doing real science) and am just catching up, so I'm not
sure which article you mean. The one about galaxy formation? How,
exactly, does that go against dark energy.

2) The discovery that there are two groups of super novae populations
that differ by color (Mentioned in the thread "Dark energy doesn't
exist?" started on Apr 13th.

Again, the question: What is the status of the paper?

In article , "Robert L.
Oldershaw" writes:

Would you agree that Paul Steinhardt, who is no slouch when it comes
to cosmology, would assess the observational support/conflict
situation for the LCDM model quite differently than you?

I agree that Paul Steinhardt would see it differently. Steinhardt, of
course, has his own axe to grind, and has made sweeping statements about
his own ekpyrotic model, many of which have been shown not to hold up.
I HIGHLY recommend the scathing critique of Steinhardt's new ideas by
Andrei Linde in

Post-Planck Cosmology, edited by C. Deffayet et al. (Oxford University
Press), 2015. ISBN: 978 0 19 872885 6.

Any good astrophysics library should have a copy. I haven't read many
proceedings cover to cover, but this is one I have. It has been well
produced.

Yes, Linde has his own axe to grind, but it appears to be much sharper
than Steinhardt's.

(There is also a huge amount of material in the online version of the
lectures. The relationship between the online material and what is in
the proceedings varies from lecturer to lecturer, but the online stuff
is mostly "slides" and the proceedings contains articles. Linde's
critique appears to have been specially written for the book version.)

In article , Steve Willner
writes:

Not related to the conclusion, the first words of the Abstract are
very strange. The authors write 'The "standard" model of cosmology
is founded on the basis that the expansion rate of the universe is
accelerating at present....' I'd say instead the standard model
(basically the Friedman equation) _contains adjustable parameters_
for the acceleration and its rate of change with time; nothing in the
model requires those to be non-zero. Observational tests show that
the acceleration is positive and its time variation (in comoving
units) smaller than can be measured.

First, I suspect that part of the problem is that "standard model" is
used differently by different people. Some intentionally define it too
strictly so that they can show that they have overturned it.

Many people do use "standard model" to mean not just the Friedmann
equation, but lambda of about 0.7 and Omega of about 0.3 (which implies
an approximately flat universe). THIS IS STILL A VERY GOOD FIT, MAYBE
EVEN THE BEST FIT, TO THE DATA, EVEN TAKING THE NEW PAPER INTO ACCOUNT.
The paper in discussion shows that non-accelerating models are not ruled
out as strongly as before.

I agree, though, that saying it is "founded" on acceleration is
misleading. This is an OBSERVATION, which is well accounted for by a
theory which is almost 100 years old.

I'm not sure what you mean by your last sentence. Despite what Bob
Kirshner appears to have said on occasion, no-one has measured
acceleration in any meaningful sense. One fits data to a model and the
acceleration is a derived quantity. So is its time variation. So
either one has "measured" both, or neither.

On Friday, June 12, 2015 at 12:43:24 PM UTC-4, Steve Willner wrote:
--
Help keep our newsgroup healthy

OMG! Here is a must-see set of assessments
given by several cosmological luminaries.

http://www.math.columbia.edu/~woit/wordpress/?p=7812

This healthy skepticism is LONG overdue.

In article ,
"Robert L. Oldershaw" writes:

On Friday, June 12, 2015 at 12:43:24 PM UTC-4, Steve Willner wrote:
--
Help keep our newsgroup healthy

OMG! Here is a must-see set of assessments
given by several cosmological luminaries.

http://www.math.columbia.edu/~woit/wordpress/?p=7812

This healthy skepticism is LONG overdue.

I was at a conference in January called "Beyond LambdaCDM", where many
alternatives to and extensions of the standard model were discussed.
(This was a high-profile conference with several luminaries, so anyone
who says "the establishment doesn't listen" isn't correct.) Many,
mostly young, researchers presented ideas about modifications to the
standard model, or some other theory, which could explain this or that.
However, as George Efstathiou pointed out, any alternative theory has to
explain at least as much as the "standard model" does. He then made an
interesting offer: "If your model explains everything the standard model
does, then I will give you a job."