structure of the universe

I was reading in the bathroom when I ran across an item written by
"The Newells" on Fri, 11 Jul 2003 15:16:22
GMT, which said:

Just keep in mind that Cosmology is one of the most speculative of
sciences.

The hell it is. It's elephants, all the way down.

-------------
Beady's Analogy: "A conspiracy theory is the intellectual equivalent of a Rube Goldberg machine; it is an overly-complex and dramatic alternative for an accepted adequate, simpler and more mundane explanation."

John Steinberg wrote:

smug look

Sorry to butt in here, but I just had my hair coiffed at Super Cuts and
one of the female employees was quite sure the whole thing was all
about *foundations*.

And she did show me her diploma from the Capri School of Cosmetology --
she graduated magna cum libamen.

So I think that should put this debate to rest for quite some time.

/smug look

--
-John Steinberg
email: lid

JSN News Ticker (r)
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I used to go to a place like that in Berlin (69-72), but it
was more "hands-on".

ôô
~

Thanks for a detailed and informative response. I'm not suggesting
that the work cosmologists have done is not valuable. Much of it may
stand the test of time. But what I do object to is the way that I
often see Cosmology explained to the public - in terms that imply that
we are as certain of these theories as we are, say, that classical
mechanics will make correct predictions in it's domain. You certainly
did not use these terms.

It's true that our confidence in any physical theory requires
assumptions. But in general, the closer a physical phenomenon is to
direct observation, and the more easily it can be frequently
manipulated and tested, the fewer assumptions are necessary and the
greater our confidence in those assumptions should be. Almost by
definition, neither of these conditions is very true for cosmology.
And there are, of course, more assumptions than those that you list.
Inflation for example.

As you say, if you don't make these assumptions, the current model of
Cosmology just doesn't work. I just think that as we add more and more
free variables, we should begin to give greater and greater weight and
devote resources to the possibility that the basic model needs to be
replaced. For all I know, this is happening, I just don't see much
reporting of it.

I think people should keep in mind that this is the way scientific
theories evolve - a rather simple and "beautiful" theory is developed
that explains a body of observations, then it may be stretched more
and more with all sorts of add-ons to explain anomalous observations,
until finally there is a break, and it is replaced by another "simple"
theory. An excellent example of this is the
early development of models for the orbits of the planets, with
epicycles etc.. Kuhn's excellent book "The Structure of Scientific
Revolutions" discussses this process. This may be happening with
Cosmology, or, of course, it may not.

Nicholas



Sam Wormley wrote in message ...
The Newells wrote:

Just keep in mind that Cosmology is one of the most speculative of
sciences. The ratio of free variables in cosmological models to number of
successful predictions made by the models is low when compared to other
areas of physics. Theories are in flux. One example - until 1997, as you can
see for yourself from old web sites, two possibilities were given for the
evolution of the Universe: either it would expand forever, slowed by
gravity, or it's expansion would be reversed by gravity. Then, observations
were made that suggested that the expansion is accelerating. The theories
have now been patched by postulating a huge quantity of "dark energy" in the
Universe.
The relative sparsity of data and difficulty in performing experiments
make cosmology very difficult. In my opinion, practitioners assign a much
higher level of certainty to their statements than they should, even though
they may contradict each other. One example: the author of one popular and
very respected cosmology web site has stated that COBE data gives us
definitive information about the nature of the Universe a million times
further out than we can currently see; other cosmologists take the more
prudent approach that we cannot come to definite conclusions about what is
currently outside our sight.
There is nothing wrong with modifying theories in response to
observations, of course - this is how science works. But some cosmologists,
at least, are reluctant to acknowledge that when this is done frequently and
in patchwork fashion, it suggests that the current models are weak. The
cosmologist referred to above actually states on his website that free
variables in a model that allow it to adapt to new observations represent a
strength of the model compared to models that have to be discarded if they
do not agree with new observations (the reference is to the debate between
the Big Bang and the Steady State theories). The trouble with this is that
free variables explain existing observations (that is what they are designed
to do), but they do not enhance the power of models to predict new
observations, which is the best test of the validity of a model. The model
becomes an organizing principle for data rather than something with
predictive power that reflects the underlying reality at some level.
To a greater extent than other sciences, Cosmology seems to be a loosely
connected and changing body of observations and free variables. The
observations that we have been getting in recent years are very exciting,
and I give lots of weight to them. I give much less weight to the theories -
I try to see cosmological theories for what they a the best that a small
group of researchers has been able to do with sparse data and almost no
opportunity to perform experiments.


Ref: http://math.ucr.edu/home/baez/TWF.html
Paraphrasing from Baez - Week 196 and Wright's WMAP News:

First of all, we only "know" anything about the world on the basis of
various assumptions. If our assumptions turn out to be wrong, our
"knowledge" may turn out to be wrong too. Even worse, our favorite
concepts may turn out to be meaningless, or meaningful only under some
restrictions.

So, when we talk about what happened in the first microsecond after
the Big Bang, we're not claiming absolute certainty. Instead, we're
using various widely accepted assumptions about physics to guess what
happened. Given these assumptions, the concept of "the first
microsecond after the Big Bang" makes perfect sense. But if these
assumptions are wrong, the whole question could dissolve into
meaninglessness. That's just a risk we have to run. What are these
assumptions, exactly? They include:

1. General Relativity
2. the Standard Model of particle physics supplemented by
3. a nonzero cosmological constant, or more generally some form of
"dark energy"
4. some form of "cold dark matter".

Assumptions 3 and 4 are the ones most people like to worry about,
because our only evidence for them comes from cosmological
observations, and if they're true, they probably require some sort of
modification of the Standard Model. But if we don't make these
assumptions, our model of cosmology just doesn't work... while if we
*do*, it seems to work quite well.

In fact, the WMAP experiment gives a lot of new evidence that it works
surprisingly well.

1. The polarization of the microwave background anisotropy coming
from scattering by electrons 200 million years after the Big Bang
has been detected. This is evidence for an early generation of
stars existing 4 to 5 times earlier than any object yet observed.

2. The WMAP data agree with previous work showing the Universe is
flat and in an accelerating expansion.

3. The WMAP data give the most precise values for the density of
ordinary [baryonic] matter made of protons and neutrons: 0.4
yoctograms per cubic meter, and for the total of dark and baryonic
matter: 2.5 yoctograms per cubic meter. These correspond to
omega_b = 0.0224 +/- 0.0009 and omega_m = 0.135 +/- 0.009.

4. The WMAP data give the most precise value for the age of the
Universe: 13.7 +/- 0.2 Gyr. The Hubble constant is Ho = 71 +/- 4
km/sec/Mpc, and the vacuum energy density corresponds to lambda =
0.73 +/- 0.04.

-Sam Wormley
http://edu-observatory.org/eo/cosmology.html

(Nicholas) wrote in message . com...
[snip]
I think people should keep in mind that this is the way scientific
theories evolve - a rather simple and "beautiful" theory is developed
that explains a body of observations, then it may be stretched more
and more with all sorts of add-ons to explain anomalous observations,
until finally there is a break, and it is replaced by another "simple"
theory. An excellent example of this is the
early development of models for the orbits of the planets, with
epicycles etc.. Kuhn's excellent book "The Structure of Scientific
Revolutions" discussses this process. This may be happening with
Cosmology, or, of course, it may not.

Nicholas

[rest snipped]

Woah - I would disagree about Kuhn's old book. His earlier book on
Kepler (if memory serves correct) was better and more precise. But
_Structure of Scientific Revolutions_ is rather outdated, at least as
far as academic consensus goes. He oversimplifies the process of
science -- even for the shift to the heliocentric model -- quite a
bit, then overgeneralizes to other scientific processes. Rarely is
there a replacement of a single theoretical model by another
theoretical model wholesale (as Kuhn seems to imply). I believe the
rest of your post is closer to the point -- that scientists continue
to fine tune and tweak the model we have now.

BTW - as if all of that is not enough, we can blame this book for the
ubiquitous (ab)use of the term "paradigm shift" among brain-dead MBA's
trying to "think out of the box" (while remaining firmly ensconsed in
said box)...

socalsw