In article ,
Nicolaas Vroom writes:
But they should demonstrate dark matter based on observations.

The video
http://vimeo.com/64868713# described at http://arxiv.org/abs/1306.0091
is an _illustration_ of current knowledge of galaxy positions,
masses, and motions. It isn't meant to demonstrate dark matter,
though as far as I can tell, the results are consistent with the
standard dark matter picture. In particular, galaxies exist
preferentially where dark matter is densest.

The matter inferred from galaxy motions should include both
vissible and darkmatter. If there is agreement then there is no
dark matter involved.

That second sentence seems to have an extra "no" in it, but the first
sentence is a misunderstanding. The video shows the _observed_
motions based on observations and with statistical corrections for
galaxies that cannot be observed because they are too faint or are in
the zone of avoidance. I didn't see a direct comparison with the
expected motions based on dark matter models, but there seems to be
at least qualitative agreement. Observed flows towards the Great
Attractor, for example, are larger than can be accounted for by
visible matter in that direction. (That statement doesn't come from
the video but rather from previous work.)

Part of my misunderstanding comes from using the words measuring
and calculating.

There's no real difference in practice. Be aware that the video
makes use of velocity-independent distances in order to measure (or
calculate, if you like) the peculiar velocities.

The starting sentence of the document reads:
"The large scale structure of the universe is a complex web of
clusters, filaments, and voids. "
This should be:
"etc of clusters, filaments, voids and darkmatter."

Or perhaps "...observed large scale structure...."

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