Re: WMAP: New Satellite Data On Universe's First Trillionth Second

rummij@xxxxxxxxxxx wrote:
Sam Wormley wrote:

rummij@xxxxxxxxxxx wrote:

WMAP: Foundations of the Big Bang theory
http://map.gsfc.nasa.gov/m_uni.html


Layman questions:

"The Big Bang Model is a broadly accepted theory for the origin and
evolution of our universe. It postulates that 12 to 14 billion years
ago, the portion of the universe we can see today was only a few
millimeters across."

That is incorrect... the decoupling of energy and matter creating
the CMB occurred at about 380,000 years after the BB. The universe
had expanded enormously in the first fraction of a second and had
been expanding and cooling for 380,000 years.




So WMAP is wrong about this?



Why is it only the portion "we can see"? The portion we can see is
surely only a completely arbitrary subset reflecting the conditions of
observation rather than what's actually out there.

We can see out for as long as light has had to travel in 13.7 billion
years, therefore, or observable horizon is about 13.7 billion light
years in radius.



Sure, but I don't understand how this proscribes a field for which we
would try to identify an origin or all-encompassing event. In fact,
this observation should compel us to not proscribe it as such?




"[...] the cosmic microwave background radiation, the remnant heat from
the Big Bang, has a temperature which is highly uniform over the entire
sky. This fact strongly supports the notion that the gas which emitted
this radiation long ago was very uniformly distributed."

If it appears uniform here and 2 billion light years away, does this
not suggest that it isn't homogeneous? Wouldn't you expect it to be
fainter here, after 2 billion years of additional cooling?

You are assuming that there is some center... when in fact all points
in the universe are equally the center.



Sorry, I don't understand how that assumes a centre. Help me out here.
Is the background radiation cooling? If so, and if it was homogeneous,
wouldn't you expect it to be more intense in observations of distant
regions?



No Center
http://www.astro.ucla.edu/~wright/nocenter.html

Also see Ned Wright's Cosmology Tutorial
http://www.astro.ucla.edu/~wright/cosmolog.htm
http://www.astro.ucla.edu/~wright/cosmology_faq.html

WMAP: Foundations of the Big Bang theory
http://map.gsfc.nasa.gov/m_uni.html

WMAP: Tests of Big Bang Cosmology
http://map.gsfc.nasa.gov/m_uni/uni_101bbtest.html




"Because the universe has a finite age (~13.7 billion years) we can
only see a finite distance out into space: ~13.7 billion light years.
This is our so-called horizon."

So ... the things we are observing at a distance of 13.7b light years
appear as they were at about the time of the Big Bang? What are we
seeing when we perceive an apparent void beyond that?

We can't see beyond that observable horizon... and light hasn't had
time to travel further.



But the fact that we can't see is also indicative of a circumstance,
huh? Ie. there is nothing old enough out there to have generated
radiation long enough ago for it to have reached us. So I take it we
can we surmise that the region beyond the horizon was a void > 13.7
billion years ago?




"The Big Bang Model does not attempt to describe that region of space
significantly beyond our horizon - space-time could well be quite
different out there."



The only reason I can think of to even imagine that it would be
different would be because we are conscious that our description of
space-time is actually a description of how we observe and think,
rather than how things really are.



Physics News Update -- Number 685, May 12, 2004
by Phil Schewe and Ben Stein
Ref: http://www.aip.org/pnu/2004/685.html

Our Universe Has a Topology Scale of at least 24 GPC

Our universe has a topology scale of at least 24 Gpc, or
about 75 billion light years, according to a new analysis
of data from the Wilkinson Microwave Anisotropy
Probe (WMAP).

What does this mean? Well, because of conceivable
hall-of-mirrors effects of spacetime, the universe might
be finite in size but give us mortals the illusion that it is
infinite. For example, the cosmos might be tiled with
some repeating shape, around which light rays might
wrap themselves over and over ("wrap" in the sense
that, as in video games, something might disappear off
the left side of the screen and reappear on the right
side).

A new study by scientists from Princeton, Montana
State, and Case Western looks for signs of such
"wrapped " light in the form of pairs of circles, in
opposite directions in the sky, with similar patterns in
the temperature of the cosmic microwave background.
If the universe were finite and actually smaller than the
distance to the "surface of last scattering" (a distance
that essentially constitutes the edge of the "visible
universe," and the place in deep space whence comes
the cosmic microwaves), then multiple imaging should
show up in the microwave background.

But no such correspondences appeared in the analysis.
The researchers are able to turn the lack of recurring
patterns into the form of a lower limit on the scale of
cosmic topology, equal to 24 billion parsecs, a factor of
10 larger than previous observational bounds. (Cornish,
Spergel, Starkman, Komatsu, Physical Review Letters,
upcoming article; contact Neil Cornish, 406-994-7986,
corn...@xxxxxxxxxxxxxxxxxxxx)





Why on earth should it be? Unless our understanding of space-time in
the observable field is just as much a function of the conditions of
observation as how it actually is. In other words, the Big Bang Model
is just as easily understood as a model of human thought and
perception, as of the origin of the universe.


Isn't everything?


It can be, I guess, but there's not always a whole lot of point to
doing that. You can undermine the applied physics of engineering just
the same way, but why would you? It works fine.

Another two statements from the WMAP site:

"The Big Bang Model is a broadly accepted theory for the origin and
evolution of our universe."

but then

"It is beyond the realm of the Big Bang Model to say what gave rise to
the Big Bang."

So BBM is actually an attempt to describe *one* event that shaped the
part of the universe that is within the horizon, but was not
necessarily the "origin of the universe" at all?



Who knows whether the BB is a "local" event or not?

The BB model, supported by much evidence, says that the universe was
hotter, smaller and denser in the past.... And you know the rest from
the WMAP web site and other sources.

A point I want to stress is the source of the CMB. As the universe
expanded and cooled... there eventually came a time, about 380,000 years
after the BB, that the temperature and density dropped, such that photons
where freed from the confinement of matter *everywhere* in the universe
bathing *everywhere* with those photons. Past, present, or future
analysis of those the photons (we currently label CMB) allows some
understanding of what the universe was like at 380,000 years and infer
conditions before that epoch.


.

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