Slashdot Mirror
Scientists Complete Universe Millennium Simulation
james tech writes "The Virgo Consortium recently completed its massive "Millennium Simulation", tracing the universe's evolution from its early origins to present day. To simplify the computations, they considered only dark matter which composes most of the universe. Using a 512-node cluster with IBM processors, the group produced over 20 terabytes of data with some of the most breathtaking images of the universe never seen. A visible matter simulation is underway, at a lower resolution."
a good one is gravitational lensing by massive clusters -- a lens analysis of all the arcs seen in, for example, a cluster, can be used to infer the mass of the cluster, and hence see that it is inconsistent with the mass of all the luminous matter. i.e. dark matter
http://www.mirrordot.org/stories/bdfc0ad7cef604a1a f6b98722b0f530f/index.html
Sigs are for the weak.
Also, by measuring the expansion rate of the universe over a very long time (ie. billions of years), and making observations of the Cosmic Microwave Backgound (CMB, the left over radiation from around 300000 years after the Big Bang) we can calculate the amount of matter it must contain. Then from models of the Big Bang and the CMB observations we can also find the amount of 'normal' matter (ie atoms), which comes to about 4% of the so called 'critical density', which is the amount of matter/energy required to have the universe be spatially flat (expands forever but tends toward zero expansion rate as time goes to infinity)
Since the amount of matter is measured to be around 25% this means dark matter must be around 20% of the critical density.
Incidentally, this also means that 75% of the energy/matter in the universe is 'dark energy', since the cosmic microwave background indicates the universe is almost exactly flat.
However, the importance of each constituent changes over time because essentially the dark energy is proportional to the size of the universe and when it was much smaller the matter was more concentrated so it had a far greater influence. Therefore for studies of the early evolution of the universe the dark energy is unimportant, and since dark matter is most of the total matter the models can just use dark matter alone. At present, however, the dark energy appears to be causing an acceleration of the expansion rate, which is seen using distant supernovae. This is how the 75% figure is worked out.
NB: Nobody can explain what the dark matter or dark energy is right now! This is by far the most important problem in Cosmology, and there are many , many competing theories.
Your question is meaningless. There is no "before" the big bang, because time AND space began at that point. "Prior" to the big bang is about as meaningful as asking what point on the Earth's surface is the center of the world.
There is no known way--and likely never will be--to know anything about existance outside of the post-big bang observable universe, other than indulging in wild and baseless speculation.