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Expanding universe

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ORFNUGEN6

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Jun 25, 1999, 3:00:00 AM6/25/99
to
Because the universe is expanding, galaxies and stars are racing
away from each other.

Does this also mean that the distance between the Earth and the
moon is getting greater? What about the distance between
the nucleus of a hydrogen atom and its electron? What
about the wavelength of light? Why should stars be moving
apart and not planets? Is all of space expanding or not?

You say the universe is getting bigger in another dimension, but
distances in our universe remain the same. Then why should an
expanding universe cause galaxies and stars to become more
distant?

Can someone give me a Flatland analogy?

If our universe is really expanding, all distances ought to be
getting larger. If Flatland expands, all its creatures become
bigger. And what becomes the constant, standard measure?
Isn't size relative?


[Moderator's note: According to modern cosmological models, the distances
between distant galaxies are increasing-- but the sizes of the galaxies are
not increasing, nor are the sizes of atoms inside them. There is a very
good Relativity FAQ entry that talks about this in some detail:

http://math.ucr.edu/home/baez/physics/expanding_universe.html

-MM]


Charles W. Shults III

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Jun 25, 1999, 3:00:00 AM6/25/99
to

ORFNUGEN6 wrote:
>
> Because the universe is expanding, galaxies and stars are racing
> away from each other.
>
> Does this also mean that the distance between the Earth and the
> moon is getting greater?

It is, but not for that reason. It's being driven
by loss of angular momentum of the Earth. It is being
transferred to the orbital motion of the Moon. This
will result in longer days for us, but only after many
millions of years will this be significant.

> What about the distance between
> the nucleus of a hydrogen atom and its electron?

No. This is determined by the wave formula for the
electron and the fact that it is a self-interfering
structure. The distance is a constant because it is
based on physical values (also constant) that do not
change, such as mass, charge, etc.
The same is true for solid objects. For them to
expand, a tension between the component atoms would
be seen. Since the effect is so small, there isn't
even a thermal effect present (from bonds elastically
resisting the tug of spatial expansion).
Maybe in a BEC properly isolated, such an effect
could be measured. It might take a lot of the stuff,
though.

> What
> about the wavelength of light?

Such an effect locally is far too small to measure.
Over cosmic distances, it's one source of red shift.
It's the "recessional velocity" of other galaxies.

> Why should stars be moving
> apart and not planets?

Actually, the planets are moving apart, but at such
a tiny scale that the larger chaotic components of
multi-body gravitational perturbation swamp them out.

> Is all of space expanding or not?

Yes. Scale is everything here, though.

> You say the universe is getting bigger in another dimension, but
> distances in our universe remain the same. Then why should an
> expanding universe cause galaxies and stars to become more
> distant?

Galaxies are large enough (and their distances also
large enough) to show the effect clearly. Solar and
stellar distances are not. Imagine the following scenario.
You know that your home expands and contracts each day as
the temperature increases from morning to evening, then
drops again after sunset. You could easily measure this
effect with a laser interferometer and a pair of mirrors,
one on each end of the building. This is because the effect
is cumulative over the entire structure.
However, if you were to measure a patch of one square
millimeter with an optical microscope, you would have no
hope of seeing the effect. Locally, it's too weak to see.
The exact analogy holds for our solar system versus some
distant galaxy.

>
> Can someone give me a Flatland analogy?

Sprinkle bb shot over a 10 kilometer rubber sheet
and stretch the sheet 1 millimeter. The shot will
certainly move apart a little, and you know they must.
However, they will not expand and they will only feel
a shift of one ten millionth of their footprint.
Very subtle.

>
> If our universe is really expanding, all distances ought to be
> getting larger.

Yes, but corrective effects come into play as
explained above.

> If Flatland expands, all its creatures become
> bigger.

No, their atoms remain the same size and they remain
the same size. The space "slips out from under them",
so to speak.

> And what becomes the constant, standard measure?

It's based on physical constants. No problem.

> Isn't size relative?

So they say...


>
> [Moderator's note: According to modern cosmological models, the distances
> between distant galaxies are increasing-- but the sizes of the galaxies are
> not increasing, nor are the sizes of atoms inside them. There is a very
> good Relativity FAQ entry that talks about this in some detail:
>
> http://math.ucr.edu/home/baez/physics/expanding_universe.html
>
> -MM]

Cheers!

Chip Shults


Prigator

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Jun 26, 1999, 3:00:00 AM6/26/99
to
orfnugen6 asks:

>Does this also mean that the distance between the Earth and the
>moon is getting greater? What about the distance between
>the nucleus of a hydrogen atom and its electron? What

>about the wavelength of light?

>Can someone give me a Flatland analogy?

>And what becomes the constant, standard measure?
>Isn't size relative?

You almost answered your own question. If everything in the universe is
expanding at the same rate, from galaxies to atoms, then the difference would
not be detectable to us. Expanding relative to what? Your ruler is expanding
at the same rate as the stars in Orion, so you would see no change.

We do see change. Red shift and all. Take it from there and cogitate some
more.

Doug Chandler


FEDERICO SURINGAR

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Jun 28, 1999, 3:00:00 AM6/28/99
to
The theory of the expansion of the Universe is based on the fact that the
light emitted by the most distant galaxies has a red shift doppler effect,
indicating that there are moving away from us. As far, greather de red shift
observed.
This mean that in his early stage the Universe was in expansion . But now
?.
In the calculation of the doppler effect, it was not considered that the
space (vaccum) could be an absorbing media. If some energy absorbtion occur,
an aditional red shift should be added to the red shift due to the
recession of the galaxie.
The observed wavelenght of the light emited by the galaxie is (lambda)obs,
the rest wavelenght of the emission is (lambda)o , (delta )gal is the shift
produced by the movement of the galaxie and (delta)abs is the shift produced
by the absorbtion of the intergalactic space, wich always is greather than
zero and proportional to the distance between the emitter and the observer.
(lambda)obs=(lambda)o+(delta)abs +(delta)gal
In this way we still observe a red shift (lambda)obs > (lambda)o ) when
(delta)gal has negative values ( blue shift)
This explanation was to show that at this time we dont't know if the
Universe is expanding or contracting, as some blue shift could arise despite
the astronomers still measuring red shifts.
Federico J.Suringar suri...@mandic.com.br

ORFNUGEN6 <orfn...@aol.com> escreveu nas notícias de
mensagem:19990622161350...@ng-fr1.aol.com...

[Moderator's note: Lots of quoted text deleted by person whose job it isn't
to delete lots of quoted text. -TB]

Jack Martinelli

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Jun 28, 1999, 3:00:00 AM6/28/99
to
Prigator wrote in message <19990625181822...@ng-fa1.aol.com>...

>orfnugen6 asks:
>>Does this also mean that the distance between the Earth and the
>>moon is getting greater? What about the distance between
>>the nucleus of a hydrogen atom and its electron? What
>>about the wavelength of light?
>
>>Can someone give me a Flatland analogy?
>
>>And what becomes the constant, standard measure?
>>Isn't size relative?
>
>You almost answered your own question. If everything in the universe is
>expanding at the same rate, from galaxies to atoms, then the difference
would
>not be detectable to us. Expanding relative to what? Your ruler is
expanding
>at the same rate as the stars in Orion, so you would see no change.


Yep. And an equivalent way of saying this is that matter is shrinking wrt
the cosmos. Which implies an equivalent *other view* of the big-bang; the
universe began as a kind of collapse of matter (like a black hole). The
other alternative - but equivalent - views go on. The one I like best is
that of a reverse inflation.

Regards

Jack Martinelli

http://www.martinelli.org

Martin Hardcastle

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Jun 28, 1999, 3:00:00 AM6/28/99
to
In article <7l0n89$5v9$1...@agate.berkeley.edu>,

Charles W. Shults III <aic...@gdi.net> wrote:
> Actually, the planets are moving apart, but at such
>a tiny scale that the larger chaotic components of
>multi-body gravitational perturbation swamp them out.

This is misleading. Distances to bodies in the Solar system are _not_
increasing as a result of the Hubble expansion, according to standard
theory; gravitationally bound systems are decoupled from the Hubble
flow.

This is explained in more detail in the FAQ entry which one of our
esteemed moderators has already referred the original questioner to:

http://math.ucr.edu/home/baez/physics/expanding_universe.html

Martin
--
Martin Hardcastle Department of Physics, University of Bristol
Be not solitary, be not idle


Matt McIrvin

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Jun 29, 1999, 3:00:00 AM6/29/99
to
In article <7l0n89$5v9$1...@agate.berkeley.edu>, aic...@gdi.net wrote:

[about solid objects not expanding with the universe]

> The same is true for solid objects. For them to
>expand, a tension between the component atoms would
>be seen. Since the effect is so small, there isn't
>even a thermal effect present (from bonds elastically
>resisting the tug of spatial expansion).
> Maybe in a BEC properly isolated, such an effect
>could be measured. It might take a lot of the stuff,
>though.

It's a bit more complicated than that. Whether such a "tug" exists or not
*at all* is, I think, an open question.

In a standard FRW cosmology, there is no "tug of spatial expansion" at all
inside of a garden-variety solid object. Space is not quite like a rubber
sheet; it expands because the objects in it are moving apart on the
largest scales, but that expansion does not itself exert the slightest tug
on your body or your planet. There is an imperceptibly tiny gravitational
pull from distant galaxies, but since they are spherically arranged about
you, the average cosmological effect is nil-- there is no cosmological
tide stretching you out, just some random effects from the
inhomogeneities.

However, some measurements seem to indicate that there is a nonzero
cosmological constant-- a kind of inflationary force everywhere in space
that might come from energy in the vacuum, or from effects beyond our
understanding. In that case, I think that there *would* be an immeasurably
tiny expansionary force acting on solid objects, though I haven't thought
much about the nature of it. Certainly it would be no match for atomic
bonds.

--
Matt McIrvin http://world.std.com/~mmcirvin/


alist...@3dresearch.com

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Jun 29, 1999, 3:00:00 AM6/29/99
to
[Moderator's note: Unnecessary quoted text deleted. -P.H.]

> [Moderator's note: According to modern cosmological models, the distances
> between distant galaxies are increasing-- but the sizes of the galaxies are
> not increasing, nor are the sizes of atoms inside them. There is a very
> good Relativity FAQ entry that talks about this in some detail:
>
> http://math.ucr.edu/home/baez/physics/expanding_universe.html

The moderator refered to the site with such a statement:
"The observation is Hubble's redshift law.

In 1929, Hubble reported that the light from distant galaxies is
redshifted. If you interpret this redshift as a Doppler shift, then the
galaxies are receding according to the law:

(velocity of recession) = H * (distance from Earth)"

[Moderator's note: The poster means that this statement is contained at
the cited URL. -P.H.]

There is no basis to "interpret this redshift as a Doppler shift".

--
Ali
http://www2.3dresearch.com/~alistolmar

[Moderator's note: As usual, the inclusion of a URL which is not the
main point of a post does not imply any approval by the moderators. -P.H.]

Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.


bu...@pac2.berkeley.edu

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Jun 29, 1999, 3:00:00 AM6/29/99
to
In article <7l0n89$5v9$1...@agate.berkeley.edu>,
Charles W. Shults III <aic...@gdi.net> wrote:

> The same is true for solid objects. For them to
>expand, a tension between the component atoms would
>be seen. Since the effect is so small, there isn't
>even a thermal effect present (from bonds elastically
>resisting the tug of spatial expansion).

I interpret this to mean that there is in principle a tension inside
of a solid due to the expansion of space, but that it's too small to
measure. If that's what you mean, then, according to our best
available theories, it's wrong. As far as we know, there is not, even
in principle, any such tension. Space, locally, is not expanding AT
ALL as far as we can tell. The Hubble expansion only occurs on large
scales (much larger than a galaxy).

The same goes for the solar system: the Hubble expansion does not
pull the planets apart at all. It's not that the effect is too
small to measure; according to the theory, it's not even there
to begin with.

When you apply general relativity to the expanding Universe, what you
find is that regions of space with large enough densities start to
clump together and "fall out" of the expansion. Our galaxy -- and
even our local group of galaxies -- did that long ago. Space
in the local group isn't expanding anymore.

>> Is all of space expanding or not?
>
> Yes. Scale is everything here, though.

No. See the FAQ entry:


>> http://math.ucr.edu/home/baez/physics/expanding_universe.html

-Ted


Phillip Helbig

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Jun 29, 1999, 3:00:00 AM6/29/99
to
In article <7l5g55$paj$1...@nnrp1.deja.com>, alist...@3dresearch.com writes:

> The moderator refered to the site with such a statement:
> "The observation is Hubble's redshift law.
>
> In 1929, Hubble reported that the light from distant galaxies is
> redshifted. If you interpret this redshift as a Doppler shift, then the
> galaxies are receding according to the law:
>
> (velocity of recession) = H * (distance from Earth)"
>
> [Moderator's note: The poster means that this statement is contained at
> the cited URL. -P.H.]
>
> There is no basis to "interpret this redshift as a Doppler shift".

True. Actually, it's sort of OK at this distance, since velocity IS
proportional to distance, but it's not an observable velocity and not an
observable distance. At small distances, all distances are degenerate,
so one can get the right answer using the wrong distance.

It is wrong to use the Doppler formula at low redshift to calculate the
expansion velocity (but it does give you the right answer, as for
example does Bohr's atom model for the hydrogen spectrum, even though we
know it is a wrong model).

It is very wrong to say that the cosmological redshift is a Doppler
shift.

It is not even wrong (i.e. so wrong it's hard to see what was supposed
to have been right) to use the relativistic Doppler formula at large
redshift.

Easiest proof of the last statement is that the relativistic Doppler
formula does not contain any cosmological parameters, while of course
the velocity, however it is defined, will depend on them. Also, there
is no distance (of the many distances in cosmology, all of which we can
calculate as a function of redshift) whose temporal derivative (i.e. a
velocity) is given by the relativistic Doppler formula.

This point has been cleared up quite well by Edward Harrison in the
references below my signature.


--
Phillip Helbig Email ......... p.he...@jb.man.ac.uk
Nuffield Radio Astronomy Laboratories Tel. ... +44 1477 571 321 (ext. 2635)
Jodrell Bank Fax ................ +44 1477 571 618
Macclesfield Telex ................ 36149 JODREL G
UK-Cheshire SK11 9DL Web ... http://www.jb.man.ac.uk/~pjh/

************************ currently working at *******************************

Kapteyn Instituut Email (above preferred) hel...@astro.rug.nl
Rijksuniversiteit Groningen Tel. ...................... +31 50 363 4067
Postbus 800 Fax ....................... +31 50 363 6100
NL-9700 AV Groningen
The Netherlands Web ... http://gladia.astro.rug.nl/~helbig/

My opinions are not necessarily those of either of the above institutes.

===============================================================================

@ARTICLE {EHarrison93a,
AUTHOR = "Edward R. Harrison",
TITLE = "The Redshift-Distance and Velocity-Distance
Laws",
JOURNAL = APJ,
YEAR = "1993",
VOLUME = "403",
NUMBER = "1",
PAGES = "28"
}

@BOOK {EHarrison81a,
AUTHOR = "Edward R. Harrison",
EDITOR = "",
TITLE = "Cosmology, the Science of the Universe",
PUBLISHER = "Cambridge University Press",
YEAR = "1981",
ADDRESS = "Cambridge"
}

james dolan

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Jun 29, 1999, 3:00:00 AM6/29/99
to bu...@pac2.berkeley.edu
ted wrote:

-In article <7l0n89$5v9$1...@agate.berkeley.edu>,
-Charles W. Shults III <aic...@gdi.net> wrote:
-
-> The same is true for solid objects. For them to
->expand, a tension between the component atoms would
->be seen. Since the effect is so small, there isn't
->even a thermal effect present (from bonds elastically
->resisting the tug of spatial expansion).
-
-I interpret this to mean that there is in principle a tension inside
-of a solid due to the expansion of space, but that it's too small to
-measure. If that's what you mean, then, according to our best
-available theories, it's wrong. As far as we know, there is not, even
-in principle, any such tension. Space, locally, is not expanding AT
-ALL as far as we can tell. The Hubble expansion only occurs on large
-scales (much larger than a galaxy).
-
-The same goes for the solar system: the Hubble expansion does not
-pull the planets apart at all. It's not that the effect is too
-small to measure; according to the theory, it's not even there
-to begin with.
-
-When you apply general relativity to the expanding Universe, what you
-find is that regions of space with large enough densities start to
-clump together and "fall out" of the expansion. Our galaxy -- and
-even our local group of galaxies -- did that long ago. Space
-in the local group isn't expanding anymore.


i can't tell whether you're addressing the same question that shults
was addressing. i assume shults was talking about the case of a small
solid object isolated in intergalactic space. what happens in that
case? i couldn't tell from your answer whether you were disagreeing
with shults even in that case.


[Moderator's note: According to GR, if there's no cosmological
constant, there's no stretching stress on the object due to the
expansion of space. The only gravitational effect is the (presumably
tiny) gravitational attraction tending to hold the object together.
If there's a cosmological constant, then (I think) there is in
principle a minuscule stress trying to make the object expand,
although of course interatomic forces would prevent it from actually
expanding. -TB]

Pedro J. Hernandez

unread,
Jul 2, 1999, 3:00:00 AM7/2/99
to
Maybe the paper below has something to say on this discussion

F. I. Cooperstock, V. Faraoni, D. N. Vollick 1998. The influence of the
cosmological expansion on local systems. astro-ph/9803097

cheers

Pedro J. Hernandez
ph...@correo.rcanaria.es


alist...@3dresearch.com

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Jul 14, 1999, 3:00:00 AM7/14/99
to
In article <7lacbu$cvd$1...@info.service.rug.nl>,

p.he...@jb.man.ac.uk wrote:
> In article <7l5g55$paj$1...@nnrp1.deja.com>, alist...@3dresearch.com
writes:
>
> > There is no basis to "interpret this redshift as a Doppler shift".
>
> True. Actually, it's sort of OK at this distance, since velocity IS
> proportional to distance....

Not "velocity", but the observed redshift is proportional to the
distance. There is no observation supporting the assumption that the
red shift - on which the Hubble law is based on - is being caused by
any motion or ballooning or any sort of EXPANSION.

> It is wrong to use the Doppler formula at low redshift to calculate the
> expansion velocity (but it does give you the right answer, as for
> example does Bohr's atom model for the hydrogen spectrum, even though we
> know it is a wrong model).
>
> It is very wrong to say that the cosmological redshift is a Doppler
> shift.
>
> It is not even wrong (i.e. so wrong it's hard to see what was supposed
> to have been right) to use the relativistic Doppler formula at large
> redshift.

[...]

So, where the "expanding Universe" comes from?
--
Ali
http://www2.3dresearch.com/~alistolmar


Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.


[Moderator's note: Actually, there is considerable observational
evidence supporting the expansion hypothesis for the cosmological
redshift. A good discussion of the problems with the alternatives is
available at

http://www.astro.ucla.edu/~wright/cosmolog.htm

-MM]

Phillip Helbig

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Jul 15, 1999, 3:00:00 AM7/15/99
to
In article <7lm2rn$eu4$1...@nnrp1.deja.com>, alist...@3dresearch.com writes:
> In article <7lacbu$cvd$1...@info.service.rug.nl>,
> p.he...@jb.man.ac.uk wrote:
> > In article <7l5g55$paj$1...@nnrp1.deja.com>, alist...@3dresearch.com
> writes:
> >
> > > There is no basis to "interpret this redshift as a Doppler shift".
> >
> > True. Actually, it's sort of OK at this distance, since velocity IS
> > proportional to distance....
>
> Not "velocity", but the observed redshift is proportional to the
> distance.

Within the context of a homogeneous and isotropic expanding universe, it
is trivial to show that velocity is proportional to distance. This does
not need any physics. If the physics is GR, this distance is the proper
distance and the velocity is it's derivative with respect to cosmic time.
This is all completely standard fare and there is no debate about it.

Neither the proper distance nor the corresponding velocity are directly
observable. So at high redshift, the situation is complicated. At low
redshift, all distance measures coincide, so AT LOW REDSHIFT one can use
the Doppler formula to ge the expansion velocity from redshift. Since
the distances are degenerate here, it doesn't matter which distance
you're talking about. However, this doesn't mean that the redshift is
CAUSED by the Doppler effect any more than the fact that Bohr's atom
model gives the right hydrogen spectrum proves that his model is correct.
(The cosmological redshift is not caused by the Doppler effect and
Bohr's atom model is not what an atom is really like.)

> There is no observation supporting the assumption that the
> red shift - on which the Hubble law is based on - is being caused by
> any motion or ballooning or any sort of EXPANSION.

Depends on what you mean by a supporting observation. It occurs
naturally within GR and there is absolutely nothing to indicate that GR
is not a valid description in the regime we're talking about.



> [Moderator's note: Actually, there is considerable observational
> evidence supporting the expansion hypothesis for the cosmological
> redshift. A good discussion of the problems with the alternatives is
> available at
>
> http://www.astro.ucla.edu/~wright/cosmolog.htm

Yes, a great source of info.
> >


Gerry Quinn

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Jul 25, 1999, 3:00:00 AM7/25/99
to
In article <7mi4c0$e1i$2...@info.service.rug.nl>, p.he...@jb.man.ac.uk wrote:

>> There is no observation supporting the assumption that the
>> red shift - on which the Hubble law is based on - is being caused by
>> any motion or ballooning or any sort of EXPANSION.
>
>Depends on what you mean by a supporting observation. It occurs
>naturally within GR and there is absolutely nothing to indicate that GR
>is not a valid description in the regime we're talking about.
>
>> [Moderator's note: Actually, there is considerable observational
>> evidence supporting the expansion hypothesis for the cosmological
>> redshift. A good discussion of the problems with the alternatives is
>> available at
>>
>> http://www.astro.ucla.edu/~wright/cosmolog.htm
>
>Yes, a great source of info.
>> >

I just came here to ask the same question: What is the observational
evidence for the expanding universe? For example, are distant galaxies
observed to be more densely clustered? Is there anywhere where such
evidence - if there is any, other than the redshift - is collected?

- Gerry Quinn


Phillip Helbig

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Aug 3, 1999, 3:00:00 AM8/3/99
to
In article <8Cpm3.300$Ua3...@news.indigo.ie>, ger...@indigo.ie (Gerry Quinn) writes:

> >> [Moderator's note: Actually, there is considerable observational
> >> evidence supporting the expansion hypothesis for the cosmological
> >> redshift. A good discussion of the problems with the alternatives is
> >> available at
> >>
> >> http://www.astro.ucla.edu/~wright/cosmolog.htm
> >
> >Yes, a great source of info.
> >> >
>
> I just came here to ask the same question: What is the observational
> evidence for the expanding universe? For example, are distant galaxies
> observed to be more densely clustered? Is there anywhere where such
> evidence - if there is any, other than the redshift - is collected?

It depends on what one means by `observational evidence'. One cannot
really DIRECTLY measure things in cosmology. The best way to think of
it is that the expanding universe is the simplest---by far the
simplest---way of explaining a whole host of observations. Yes, distant
galaxies ARE more clustered, but one has to correct for their evolution.
Of course, what one measures is really some number density of objects on
the sky (subject to all the observational problems involved) and
INTERPRETS this in the context of the expanding universe. The same
expanding universe explains why (from the observation of molecular lines
etc) the CMB temperature was higher in the past. Also, things like the
theory of the origin of the light elements provide tremendous support to
the expanding universe picture.

The bottom line is that while a devil's advocate might argue, in a
particular case, that one has not DIRECTLY detected the expansion, the
fact remains that the expanding universe, due to its ability to tie so
many different types of observation together, is one of our more certain
bits of scientific knowledge.

Gerry Quinn

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Aug 6, 1999, 3:00:00 AM8/6/99
to
In article <7o2jke$av7$1...@info.service.rug.nl>, p.he...@jb.man.ac.uk wrote:
>In article <8Cpm3.300$Ua3...@news.indigo.ie>, ger...@indigo.ie (Gerry Quinn)
> writes:
>
>> >> [Moderator's note: Actually, there is considerable observational
>> >> evidence supporting the expansion hypothesis for the cosmological
>> >> redshift. A good discussion of the problems with the alternatives is
>> >> available at
>> >>
>> >> http://www.astro.ucla.edu/~wright/cosmolog.htm
>> >
>> >Yes, a great source of info.
>> >> >
>>
>> I just came here to ask the same question: What is the observational
>> evidence for the expanding universe? For example, are distant galaxies
>> observed to be more densely clustered? Is there anywhere where such
>> evidence - if there is any, other than the redshift - is collected?
>
>It depends on what one means by `observational evidence'. One cannot
>really DIRECTLY measure things in cosmology. The best way to think of
>it is that the expanding universe is the simplest---by far the
>simplest---way of explaining a whole host of observations. Yes, distant
>galaxies ARE more clustered, but one has to correct for their evolution.

Now _that's_ the sort of thing I'm interested in, if you can give me
references. I appreciate that the galaxies are not laid out neatly on a
grid, and the interpretation may be difficult, but I'm wondering how far
we can go along this route.

>Of course, what one measures is really some number density of objects on
>the sky (subject to all the observational problems involved) and
>INTERPRETS this in the context of the expanding universe. The same
>expanding universe explains why (from the observation of molecular lines
>etc) the CMB temperature was higher in the past. Also, things like the
>theory of the origin of the light elements provide tremendous support to
>the expanding universe picture.
>

Certainly the CMBR and H/He ratio demonstrate that every part of the
universe was at one time rather hot, and that the radiation from this
period has become redshifted by a process which applies directly to the
radiation.

>The bottom line is that while a devil's advocate might argue, in a
>particular case, that one has not DIRECTLY detected the expansion, the
>fact remains that the expanding universe, due to its ability to tie so
>many different types of observation together, is one of our more certain
>bits of scientific knowledge.
>

Candidly, I am not convinced, because I do not believe that special and
general relativity are a good model* of physical reality.
Over-ambitious layman though I may be, I think a model based on an
extended version of Lorentz Ether Theory in Galilean (flat) spacetime,
with gravity seen as a refractive field, makes more sense - especially
in the light of modern ideas about the vacuum. The cosmological
implications of such a model are that a theory similar to the 'open
inflation' theory of Martin A. Bucher et al is required. Anyway, there
is a newsgroup for relativistic matters, so I will not elaborate further
here, until I'm ready to shake the world ;)

*When I say 'not a good model', I mean there may be a better one, which
predicts much the same observations, but may differ in detail, explain
more, or be more specific about what is physically realistic. Obviously
special and general relativity do agree quite well with observations.

- Gerry Quinn

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