structure of the universe

Are you saying that the volume is infinite? Clearly, the universe is
functioning on a 3-D level even if there are other dimensions.

Ed

"Chris L Peterson" wrote in message

But it isn't even remotely like either. It has no three-dimensional shape
at
all, and no three-dimensional center.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Thu, 10 Jul 2003 17:05:49 GMT, "Edward" wrote:

Are you saying that the volume is infinite? Clearly, the universe is
functioning on a 3-D level even if there are other dimensions.

No. The Universe can have a finite volume and be unbounded (in three dimensions)
in the same way that the surface of a sphere has a finite area but is unbounded
in two dimensions (to use a common analogy.)

To use your terminology, the surface of the sphere is functioning on a 2-D level
but is embedded in three dimensions.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Hi Chris,
I know, read the book g. To test your patience just a bit more... After
travelling the requisit number of light years (in a 3-D linear direction),
would we at some point begin returning to our point of origin?

Thanks,
Ed


"Chris L Peterson" wrote in message
...
On Thu, 10 Jul 2003 17:05:49 GMT, "Edward" wrote:

Are you saying that the volume is infinite? Clearly, the universe is
functioning on a 3-D level even if there are other dimensions.

No. The Universe can have a finite volume and be unbounded (in three
dimensions)
in the same way that the surface of a sphere has a finite area but is
unbounded
in two dimensions (to use a common analogy.)

To use your terminology, the surface of the sphere is functioning on a 2-D
level
but is embedded in three dimensions.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Edward wrote:
I know, read the book g. To test your patience just a bit more... After
travelling the requisit number of light years (in a 3-D linear direction),
would we at some point begin returning to our point of origin?

That depends on the topology of the universe, as opposed to its geometry,
which tells you how it is curved. Ordinarily, we think of those things
as being intimately related; it is hard for us to imagine a surface which
is curved like a sphere, but which is not in fact topologically a sphere.
That does not mean, however, that it cannot exist.

For example, a circle is a simple closed curve in a plane. It has constant
curvature, and if you travel a distance equal to the circumference of the
circle, you return to your starting point.

However, consider a tight spring. It too has a curvature which is quite
similar to that of a circle, and if you imagine an arbitrarily tight
spring, it has a curvature which in the limit is equal to that of the
circle. Yet, if you travel a distance which is equal to the circumference
of that limiting circle, you do not return to your starting point. In
fact, you can go as far as you like and you will never return to your
starting point. This is an instance of a one-dimensional "universe" that
has a curvature like that of a circle, but is not closed and finite. It
is, instead, open and infinite. Same geometry, with respect to curvature,
but different topology, and it is the topology that tells you if you can
return to your starting point.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

On Thu, 10 Jul 2003 17:34:33 GMT, "Edward" wrote:

Hi Chris,
I know, read the book g. To test your patience just a bit more... After
travelling the requisit number of light years (in a 3-D linear direction),
would we at some point begin returning to our point of origin?

Presumably. It would be a long trip, though. Indeed, with the Universe
apparently expanding at an increasing rate, it might never be possible to get
back to the starting point, even traveling at the speed of light.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris L Peterson wrote:

On Thu, 10 Jul 2003 17:05:49 GMT, "Edward" wrote:

Are you saying that the volume is infinite? Clearly, the universe is
functioning on a 3-D level even if there are other dimensions.

No. The Universe can have a finite volume and be unbounded (in three dimensions)
in the same way that the surface of a sphere has a finite area but is unbounded
in two dimensions (to use a common analogy.)


It's four-dimensional (finite and unbounded).

On Thu, 10 Jul 2003 20:01:23 GMT, Sam Wormley wrote:


It's four-dimensional (finite and unbounded).


The various recent Superstring Theories (or the even more recent M-Theory)
suggest that the universe is actually most likely to have 10 (or in the
case of M-Theory, 11) dimensions, but please don't ask me to try and
explain why. I do know that a bunch of the worlds best Cosmologists and
Astro-Physicists are taking this quite seriously though.

Lawrence Sayre

--
My philosophy, in essence, is the concept of man as
a moral being, with his own happiness as the moral
purpose of his life, with productive achievement as
his noblest activity, and reason as his only absolute.

Ayn Rand (in the appendix to 'Atlas Shrugged')

On Thu, 10 Jul 2003 20:26:42 GMT, Lawrence Sayre wrote:

The various recent Superstring Theories (or the even more recent M-Theory)
suggest that the universe is actually most likely to have 10 (or in the
case of M-Theory, 11) dimensions, but please don't ask me to try and
explain why. I do know that a bunch of the worlds best Cosmologists and
Astro-Physicists are taking this quite seriously though.

I believe this is a possible description for the microscopic structure of the
Universe. These higher order dimensions are "folded up" into space-time,
however, so the Universe as a whole is still a 4-dimensional structure.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

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.

Nicholas


"crom" wrote in message
...
Is the shape and organization of the universe a spiral similar to our
galaxy? If this is the case does the center of the universe (origin of
the
big bang) contain a massive black hole? It seems that structure repeats
its self throughout our universe so this assumption would make sense.

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