[Phys-L] shape of the universe?

[Anthony Lapinski <alapinski@pds.org>]

Will be discussing this in my (high school) astronomy class in a few
months. Seeing conflicting results online. Density shows universe is open,
but CMB says it's flat (see below). What about evidence for closed? It
seems that a flat universe would be a special case and highly unlikely
(expansion = 0 at infinite size). Maybe the data suggested otherwise. Or do
cosmologists have biases toward a flat universe? Dark matter? Olbers'
Paradox - age and size are finite.

from WMAP/NASA:

*The WMAP <https://wmap.gsfc.nasa.gov/news/facts.html> spacecraft can
measure the basic parameters
<https://wmap.gsfc.nasa.gov/mission/sgoals_parameters.html> of the Big Bang
<https://wmap.gsfc.nasa.gov/universe/bb_theory.html> theory including the
geometry of the universe. If the universe were flat, the
brightest microwave background fluctuations
<https://wmap.gsfc.nasa.gov/universe/bb_cosmo_fluct.html> (or "spots")
would be about one degree across. If the universe were open, the spots
would be less than one degree across. If the universe were closed, the
brightest spots would be greater than one degree across.*

*Recent measurements (c. 2001) by a number of ground-based and
balloon-based experiments, including MAT/TOCO
<https://wwwphy.princeton.edu/cosmology/mat/>, Boomerang
<https://cmb.phys.cwru.edu/boomerang/>, Maxima
<https://cosmology.berkeley.edu/group/cmb/index.html>, and DASI
<https://astro.uchicago.edu/dasi/>, have shown that the brightest spots are
about 1 degree across. Thus the universe was known to be flat to within
about 15% accuracy prior to the WMAP results. WMAP has confirmed this
result with very high accuracy and precision. We now know (as of 2013) that
the universe is flat with only a 0.4% margin of error. This suggests that
the Universe is infinite in extent; however, since the Universe has a
finite age, we can only observe a finite volume of the Universe. All we can
truly conclude is that the Universe is much larger than the volume we can
directly observe.*