Flat Earthers back in charge of Cosmology?

It seems to me that the Standard FRW Model has an Achilles foot of
clay -- namely, the whole edifice is founded upon the so-called flat
universe, i.e. the flat Euclidean model of space-time. This
assumption underlies everything that is done, but it is basically just
that, an assumption, and cosmologists are (in my fevered imagination)
hoping that nobody notices. Yes, perhaps today's cosmology is being
run by a new generation of flat Earthers?

Now, of course some justification is being made for the utilization of
a flat universe paradigm. For example, it is claimed that WMAP
observations demonstrate that the universe is flat, etc. But really,
do not such conclusions follow a circular line of reasoning? It seems
to me that such calculations *assume* the flat universe to begin with,
and then *deduce* the flat universe from that -- which of course
establishes nothing.

OK, I admit it, my understanding is incomplete. But I don't see why a
flat universe is compelling from the evidence. Mathematically, as all
you erudite gentlemen know, three types of space-time are valid,
concave (spherical), flat, and convex (hyperbolic). Now, valid
mathematical models generally have corresponding physical phenomena.
Hyperbolic and spherical manifolds should have real physical
counterparts. The flat-universe paradigm denies this essential
expectation.

Simply, a hyperbolic space-time (in comparison with flat) yields a
greater number of faint close-up objects -- which is what we observe
today, and interpret an an "accelerating expansion" of a flat
universe. It is as though we interpreted the Earth as flat, but
expanding locally compared with far-away places, instead of the simple
interpretation that it is spherical. Surely, what is good enough for
the Earth should be good enough for the Universe. I thought we got
rid of the flat Earhters 400 years ago!

So I am looking for a reason to believe. What non-circular evidence
is there that the universe is flat? Or is this all just a house of
canards, er, cards?

Eric Flesch

In article ,
(Eric Flesch) writes:

It seems to me that the Standard FRW Model has an Achilles foot of
clay -- namely, the whole edifice is founded upon the so-called flat
universe, i.e. the flat Euclidean model of space-time.

Wrong. Flatness, or near-flatness, is something which is DEDUCED from
observations, not an assumption. Of course, someone else might think
that this is so well established that he assumes it when calculating
something else (e.g. galaxy formation), but it is NOT assumed when
determining the cosmological parameters.

This
assumption underlies everything that is done, but it is basically just
that, an assumption, and cosmologists are (in my fevered imagination)
hoping that nobody notices. Yes, perhaps today's cosmology is being
run by a new generation of flat Earthers?

No. There was a time, about 15 years ago, when the Einstein-de Sitter
model was assumed without good evidence. Some people just assumed it as
a working hypothesis, but the assumption was so widespread that many
people thought there was evidence for it. However, that was back in the
days when there were only 9 facts in cosmology. Now, cosmology is a
data-driven science, and the current "standard model" is a result of
observations. Note that for many people it was quite difficult to
accept the current standard model, a flat model with a positive
cosmological constant.

Now, of course some justification is being made for the utilization of
a flat universe paradigm. For example, it is claimed that WMAP
observations demonstrate that the universe is flat, etc. But really,
do not such conclusions follow a circular line of reasoning? It seems
to me that such calculations *assume* the flat universe to begin with,
and then *deduce* the flat universe from that -- which of course
establishes nothing.

No, this is simply wrong. Can you point to one example of such circular
reasoning in the literature?

OK, I admit it, my understanding is incomplete. But I don't see why a
flat universe is compelling from the evidence. Mathematically, as all
you erudite gentlemen know, three types of space-time are valid,
concave (spherical), flat, and convex (hyperbolic). Now, valid
mathematical models generally have corresponding physical phenomena.
Hyperbolic and spherical manifolds should have real physical
counterparts. The flat-universe paradigm denies this essential
expectation.

One assumes arbitrary lambda and Omega, which allow for all types of
curvature, and deduces the parameters from fits to observational data.

Again, if someone is interested in, say, the equation of state of the
universe, then he might assume flatness and present his results for the
case of the flat universe, but this is because he believes that the
flatness has already been established. However, it is not assumed for
any determination of cosmological parameters for which flatness is a
derived conclusion.

Simply, a hyperbolic space-time (in comparison with flat) yields a
greater number of faint close-up objects -- which is what we observe
today, and interpret an an "accelerating expansion" of a flat
universe.

This is true for a specific redshift. However, acceleration and
negative curvature are not degenerate. By looking at the dependence on
redshift, one can differentiate the two, and also differentiate from
other effects which lead to faintness, like dust. In particular, in the
flat accelerated case, above a certain redshift the objects become
brighter than "expected".

So I am looking for a reason to believe. What non-circular evidence
is there that the universe is flat? Or is this all just a house of
canards, er, cards?

First, no-one can seriously claim that it is exactly flat, but rather
quite near flat. There is a HUGE amount of evidence for this. In
particular, of all the various cosmological tests, once one combines 2
or 3 to derive joint constraints, non-flat models start looking
improbable.

On Tue, 20 Nov 07 09:34:19 GMT, (Eric Flesch) wrote:


So I am looking for a reason to believe. What non-circular evidence
is there that the universe is flat? Or is this all just a house of
canards, er, cards?

Like you, I find a flat universe unappealing.
Assuming your question is rhetorical, try:
http://xyz.lanl.gov/abs/0709.0886
"The scale and the substructure, i.e. 30 degree-radius rings and
voids in the distribution of the excursion sets around the
antipodes, reveal features of mirroring which cannot be
explained either via global (integrated Sachs-Wolf effect)
or local inhomogeneities of matter. The anomaly is also
not close to the apex of the CMB dipole arisen due to the
motion of the Earth i.e. of the detector. This mirroring
effect can be the first empirical signature of a Universe
with compact topology, potentially of either curvature."

and
"The mirrored structures cannot be explained simply via inte-
grated Sachs-Wolf effect or via nearby matter anomalies10, i.e.
either by means of global or local inhomogeneities. Mirrored fea-
tures however, would be expected in a Universe with a compact
topology; for examples of hyperbolic and other spaces see e.g.
ref.[11,12]. If we, indeed, deal with the first empirical signature
of a compact space, this result and this method of analysis can
open a new path towards overcoming the curvature/topology de-
generacy and revealing the genuine shape of the Universe."

These references were originally intended as a response to a Sam
Wormley post:
http://groups.google.com/group/sci.p...3b73bb43d99816

John

On Tue, 20 Nov 07, Phillip Helbig wrote:
(Eric Flesch) writes:
Now, of course some justification is being made for the utilization of
a flat universe paradigm. For example, it is claimed that WMAP
observations demonstrate that the universe is flat, etc. But really,
do not such conclusions follow a circular line of reasoning? It seems
to me that such calculations *assume* the flat universe to begin with,
and then *deduce* the flat universe from that -- which of course
establishes nothing.

No, this is simply wrong. Can you point to one example of such circular
reasoning in the literature?

I specified WMAP. My understanding is incomplete, but I doubt that
such a uniform background with a few wrinkles truly demonstrates a
flat universe. And as for the black body spectrum, it is, after all,
just a normal distribution over a logarithmic scale, so what's the big
deal? It seems to me that a lot of prior construction has gone into
any conclusion that WMAP shows a flat universe, so there's the
circularity.

Simply, a hyperbolic space-time (in comparison with flat) yields a
greater number of faint close-up objects -- which is what we observe
today, and interpret an an "accelerating expansion" of a flat
universe.

This is true for a specific redshift. However, acceleration and
negative curvature are not degenerate. By looking at the dependence on
redshift, one can differentiate the two, and also differentiate from
other effects which lead to faintness, like dust. In particular, in the
flat accelerated case, above a certain redshift the objects become
brighter than "expected".

Sure, but this can be just as easily modelled as a hyperbolic manifold
embedded in a spherical. No accelerating expansion required. And all
physically possible curvatures are reified,

First, no-one can seriously claim that it is exactly flat, but rather
quite near flat. There is a HUGE amount of evidence for this.

Sure, the universe is locally flat, but so is the Earth. So there is
HUGE evidence that the universe is flat everywhere? Evidence that is
clear and non-circular? What is the best such evidence?

On Tue, 20 Nov 07, John Bailey wrote:
" ... This mirroring
effect can be the first empirical signature of a Universe
with compact topology, potentially of either curvature."

Yes, well, a pity the effect isn't clearer, or clear enough to shake
up the flat-universe crowd. Imagine building a new instrument, and
when it is turned on, suddenly the whole geometry of the universe is
seen with crystal clarity. I suppose such a development would evoke
claustrophobic feelings in some people ("we're living in a cage!"), so
perhaps it's just as well.

(Eric Flesch) wrote:

Now, valid mathematical models generally have
corresponding physical phenomena.

That's an _extremely_ strange thing to believe about
mathematics and mathematical models. Any old piece
of nonsense most likely can be mathematically
modeled in a self-consistent way. For example a
model could possibly be created under which
Burroughs Barsoom stories were on a planet that had
breathable air, perhaps by earlier events colliding
most of the Oort cloud with Mars leaving only the
current remnant of snowballs. That model does not
make the real Mars "habitable" as usually
understood.

More than that, probably (almost certainly) a
countable infinity of "valid mathematical models"
could be created, of which the ones
realizable/realized in the physical universe would
be a subset of measure zero.

You certainly shouldn't let such a mindset drive you
to speculate that the received wisdom of cosmology
considered together with all its supporting evidence
is incorrect _merely because_ other arrangements for
some universe somewhere can be mathematically
modeled. That way lies madness.

xanthian.

In article , John Bailey
writes:

On Tue, 20 Nov 07 09:34:19 GMT, (Eric Flesch) wrote:

So I am looking for a reason to believe. What non-circular evidence
is there that the universe is flat? Or is this all just a house of
canards, er, cards?

Like you, I find a flat universe unappealing.
Assuming your question is rhetorical, try:
http://xyz.lanl.gov/abs/0709.0886
"The scale and the substructure, i.e. 30 degree-radius rings and
voids in the distribution of the excursion sets around the
antipodes, reveal features of mirroring which cannot be
explained either via global (integrated Sachs-Wolf effect)
or local inhomogeneities of matter. The anomaly is also
not close to the apex of the CMB dipole arisen due to the
motion of the Earth i.e. of the detector. This mirroring
effect can be the first empirical signature of a Universe
with compact topology, potentially of either curvature."

Note that while, from time to time, observations have been interpreted
as indicating a non-trivial topology, as far as I know none of them has
really panned out. Also, the question of non-trivial topology is more
or less independent of whether or not the universe is flat. Topology is
global; curvature is local (and, of course, in a homogeneous universe it
is everywhere the same).

In article ,
(Eric Flesch) writes:

On Tue, 20 Nov 07, Phillip Helbig wrote:
(Eric Flesch) writes:
Now, of course some justification is being made for the utilization of
a flat universe paradigm. For example, it is claimed that WMAP
observations demonstrate that the universe is flat, etc. But really,
do not such conclusions follow a circular line of reasoning? It seems
to me that such calculations *assume* the flat universe to begin with,
and then *deduce* the flat universe from that -- which of course
establishes nothing.

No, this is simply wrong. Can you point to one example of such circular
reasoning in the literature?

I specified WMAP. My understanding is incomplete, but I doubt that
such a uniform background with a few wrinkles truly demonstrates a
flat universe.

There have been many analyses of the WMAP data which DERIVE Omega and
lambda without any prior constraints. It's not just the wrinkles but
rather the scale at which they appear. Interestingly, while some
information is difficult to harvest from the CMB data, i.e. it is
(almost) degenerate with something and thus cannot be determined well
without prior assumptions, the opposite is the case for the curvature.
Flatness implies Omega + lambda = 1. The CMB alone cannot, without
additional assumptions, determine Omega and lambda well separately, but
can determine their sum quite well. This is actually a very strong
signal. (The strongest is the black-body spectrum, then the fact that
it is almost isotropic, then the dipole caused by our peculiar motion,
then the curvature signal, then come other signals.)

And as for the black body spectrum, it is, after all,
just a normal distribution over a logarithmic scale, so what's the big
deal? It seems to me that a lot of prior construction has gone into
any conclusion that WMAP shows a flat universe, so there's the
circularity.

Most other things astronomers observe do not have black-body spectra.
Even without absorption lines, stars do not have black-body spectra.
The fact that a black-body spectrum was predicted for the CMB and that
it has been observed are very significant.

First, no-one can seriously claim that it is exactly flat, but rather
quite near flat. There is a HUGE amount of evidence for this.

Sure, the universe is locally flat, but so is the Earth. So there is
HUGE evidence that the universe is flat everywhere? Evidence that is
clear and non-circular? What is the best such evidence?

You are confusing two things. First, everything is locally flat, i.e.
if the scale is small enough. That's like saying everything is linear
to first order. :-) Second, within the context of Friedmann-Lemaître
cosmology, the curvature is everywhere the same. So, when we say "the
universe is (nearly) flat", we mean that it is flat even on large
scales, not trivially flat on local scales. It is the former that WMAP
measures.

Thus spake Eric Flesch
On Tue, 20 Nov 07, Phillip Helbig wrote:
(Eric Flesch) writes:
Now, of course some justification is being made for the utilization of
a flat universe paradigm. For example, it is claimed that WMAP
observations demonstrate that the universe is flat, etc. But really,
do not such conclusions follow a circular line of reasoning? It seems
to me that such calculations *assume* the flat universe to begin with,
and then *deduce* the flat universe from that -- which of course
establishes nothing.

No, this is simply wrong. Can you point to one example of such circular
reasoning in the literature?

I specified WMAP. My understanding is incomplete, but I doubt that
such a uniform background with a few wrinkles truly demonstrates a
flat universe.

There is more to it than that. The spectrum of the "wrinkles" can be
analysed. The result can be related to the curvature of the universe.
There are a few anomalies, but basically this is a solid bit of work
based on gtr as we understand it.

And as for the black body spectrum, it is, after all,
just a normal distribution over a logarithmic scale, so what's the big
deal? It seems to me that a lot of prior construction has gone into
any conclusion that WMAP shows a flat universe, so there's the
circularity.

Not really, but it does rest on an untested assumption in gtr and one we
already know is wrong because Einstein pointed out an inconsistency.
Classical electromagnetism does not mesh with gtr, in that our
description of a classical e.m. wave from a distant source is not
consistent with the description of the same e.m. wave as given by an
observer close to that source. We also know that e.m. waves are more
accurately treated in the quantum domain. We ought to assume that the
interpretation of all measurements based on redshift from distant
sources is likely to be wrong. I have done a number of tests within the
galaxy which show that this is in fact the case, so I do not think much
weight should be put on the analysis of WMAP.

Simply, a hyperbolic space-time (in comparison with flat) yields a
greater number of faint close-up objects -- which is what we observe
today, and interpret an an "accelerating expansion" of a flat
universe.

This is true for a specific redshift. However, acceleration and
negative curvature are not degenerate. By looking at the dependence on
redshift, one can differentiate the two, and also differentiate from
other effects which lead to faintness, like dust. In particular, in the
flat accelerated case, above a certain redshift the objects become
brighter than "expected".

Sure, but this can be just as easily modelled as a hyperbolic manifold
embedded in a spherical. No accelerating expansion required. And all
physically possible curvatures are reified,

First, no-one can seriously claim that it is exactly flat, but rather
quite near flat. There is a HUGE amount of evidence for this.

Sure, the universe is locally flat, but so is the Earth. So there is
HUGE evidence that the universe is flat everywhere? Evidence that is
clear and non-circular? What is the best such evidence?

As far as I know, WMAP is the only evidence.


Regards

--
Charles Francis
moderator sci.physics.foundations.
substitute charles for NotI to email

On Wed, 21 Nov 07, Oh No wrote:
Thus spake Eric Flesch
Sure, the universe is locally flat, but so is the Earth. So there is
HUGE evidence that the universe is flat everywhere? Evidence that is
clear and non-circular? What is the best such evidence?

As far as I know, WMAP is the only evidence.

Considering the FRW model antedates WMAP (and Boomerang) by a few
decades, they would have walked a long plank over a hypothetical "flat
universe". If they really have no evidence other than that, then I
dare say a large scientific establishment has been built up on an
assumption. There's a lot of inertia there. Hey, maybe if I shout at
the big brick wall...

Hey people, IT'S A HYPERBOLIC MANIFOLD. There's NO ACCELERATING
EXPANSION. NO DARK MATTER. NO DARK ENERGY.

Imagine if people had modelled the Earth like this 500 years ago.
Local places expand compared with faraway places! Dark energy and
dark matter are used to account for the dynamic effects which we
cannot see or justify, but which must be there! Yes, this would be
the theory of the Earth today if the Flat Earthers had never relaxed
their grip. Grrr...

Hey people, IT'S HYPERBOLIC. THIS IS NOT HARD.

sigh...

[Mod. note: perhaps more argument in favour of your preferred model
would be preferable to shouting! -- mjh]