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2Physics Quote:
"The exchange character of identical particles plays an important role in physics. For bosons, such an exchange leaves their quantum state the same, while a single exchange between two fermions gives a minus sign multiplying their wave function. A single exchange between two Abelian anyons gives rise to a phase factor that can be different than 1 or -1, that corresponds to bosons or fermions, respectively. More exotic exchanging character are possible, namely non-Abelian anyons. These particles have their quantum state change more dramatically, when an exchange between them takes place, to a possibly different state." -- Jin-Shi Xu, Kai Sun, Yong-Jian Han, Chuan-Feng Li, Jiannis K. Pachos, Guang-Can Guo
(Read Full Article: "Experimental Simulation of the Exchange of Majorana Zero Modes"
)

Tuesday, July 05, 2005

The Millennium Simulation

It is called the Millennium Simulation. It was a big job undertaken by the
Virgo consortium, an international group of astrophysicists from the UK,
Germany, Canada and the US. The consortium modeled more than 10
billion particles of matter in order to trace the evolution of the
distribution of matter within a cubic region of the universe measuring
more than 2 billion light-years each side.

It kept the principal supercomputer at the Max Planck Society's
Supercomputing Centre in Garching, Germany fully occupied for more
than a month. By applying sophisticated modeling techniques to the 25
terabytes of output, Virgo scientists have simulated evolutionary
histories for the galaxies (approximately 20 million of them) that populate
this volume, and for the super-massive black holes occasionally seen as
quasars at their hearts.

The Millennium Simulation was designed to follow the evolution of the
universe from when it was just 400,000 years old (the point from which
it has been imaged using microwave telescopes) to the present day. It
has the twin goals of exploring the complex physics that gave rise to
galaxies and their central black holes and of checking that the new
paradigm for cosmic evolution emerging from this activity is consistent
with what is observed.

The Sloan Digital Sky Survey had discovered earlier a number of very
distant and bright quasars, which appear to host black holes a billion
times more massive than the sun, at a time when the universe was less
than a tenth its present age. Many astronomers considered this
observation impossible to reconcile with the gradual growth of structure
predicted by the standard models. Yet the galaxy and quasar formation
modelling found that a few massive black holes do form early enough to
account for these very rare type of quasars.

The most interesting aspect of the preliminary results is that they
demonstrate that the characteristic patterns imprinted on the
distribution of matter at early epochs should still be present - and
detectable - in the observed distribution of galaxies. Measuring these
should provide a standard measuring rod to characterise the geometry
and expansion history of the universe and so to learn about the nature
of the Dark Energy.


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