A cosmic hall of mirrors in the WMAP data

A very intriguing article that may well skew the Fermi Paradox and give
good food for a huge DC (Boinc?) project:


A cosmic hall of mirrors
http://www.physicsweb.org/articles/world/18/9/3/1


Sorry, there's rather a lot to quote. In short:

Our universe could very well be /smaller/ that the /observable/
universe. A computer search has been made to find 'ghost images' in the
microwave all sky survey data and some tantalising matches have been
found. A lot more compute power is needed to gain better matches.

Oh, and our universe might be quite small!

To make my own glib comparison, there are suspiciously similar numbers
for the number of dimensions for string and brane theory and the
topology suggested here for the universe...


Interesting stuff!

Regards,
Martin



A few snippets:

Most astronomers think that the universe is infinite, but recent
measurements suggest that it could be finite and relatively small.

.... Surprisingly, the latest astronomical data suggest that the correct
answer could be a compromise between these two ancient viewpoints: the
universe is finite and expanding but it does not have an edge or boundary.

.... In such a scenario, an object that travels away from the Earth in a
straight line will eventually return from the other side of the
universe, having been rotated by 36° in the process. Space might
therefore act like a cosmic hall of mirrors by creating multiple images
of faraway light sources, which raises new questions about the physics
of the early universe. However, this is just one possibility and other
proposals made by researchers in the expanding field of cosmic topology
include tetrahedral and octahedral spaces, flat doughnuts and an
infinite "horn-shaped" universe.

Furthermore, general relativity does not distinguish between these
possibilities because each of the three plausible cosmic geometries -
flat, hyperbolic and spherical - is consistent with many different
topologies. ... Determining the topology of the cosmos therefore
requires some physical understanding beyond relativity, in particular
concerning the way different regions of space-time are connected.

This means that an observer would see multiple images of each galaxy and
could easily misinterpret them as distinct galaxies in an endless space,
much as a visitor to a mirrored room has the illusion of seeing a crowd.
Could we, in fact, be living in such a cosmic hall of mirrors?

The surprise from the WMAP data is that the topology of space seems
indeed to be multiply connected and described by a special class of
shapes that are called "well proportioned".

Moreover, given the observed values of the mass-energy densities and of
the expansion rate of the universe, the size of the dodecahedral
universe can be calculated. We found that the smallest dimension of the
Poincaré dodecahedron space is 43 billion light-years, compared with 53
billion light-years for the "horizon radius" of the observable universe.
Moreover, the volume of this universe is about 20% smaller than the
volume of the observable universe. (There is a common misconception that
the horizon radius of a flat universe is 13.7 billion light-years, since
that is the age of the universe multiplied by the speed of light.
However, the horizon radius is actually much larger because photons from
the horizon that are reaching us now have had to cross a much larger
distance due to the expansion of the universe.)

If physical space is indeed smaller than the observable universe, some
points on the map of the cosmic microwave background will have several
copies. As first shown by Neil Cornish of Montana State University and
co-workers in 1998, these ghost images would appear as pairs of
so-called matched circles in the cosmic microwave background where the
temperature fluctuations should be the same (figure 4). This "lensing"
effect, which can be precisely calculated, is thus purely attributable
to the topology of the universe.



This violates one of the most basic principles of cosmology, that there
is no privileged position in the universe. But this principle could be
illusory, like the ant in the desert that is convinced the whole world
is filled with sand and dunes. For instance, in a flat-torus universe,
any gluing together of the opposite faces combined with a screw motion
produces pair of circles that are far from being back-to-back.
Unfortunately, the increase in the number of degrees of freedom that
results from such a scenario means that a full-circle search in the WMAP
data is beyond current computing capabilities.

In June 2004, however, Boud Roukema and colleagues at the Torun Centre
for Astronomy in Poland independently searched for circles in the WMAP
data. By only looking for back-to-back circles within a limited range of
angular sizes and neglecting all other possible matches, the computer
time was reduced drastically. Remarkably, the Polish team found six
pairs of matched circles distributed in a dodecahedral pattern and
twisted by 36°, each with an angular size of about 11°. This implied
that Ω = 1.010 ± 0.001, which is perfectly consistent with our
dodecahedral model, although the result was much less publicized than
the earlier negative results.

In fact, the statistical significance of the match still needs to be
improved, which means that the validity of the Poincaré dodecahedron
model is still open to debate. ...





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