Consider a universe in which gravity includes a repulsive force at close distances, such that this equation is true.

-How large would alpha need to be in order for the collapse of a 200,000 solar mass cluster initially spread out over 5000 light years to be significantly altered?

-Users should implement a standard N-body code (see this challenge) with the above force law, modified to run in parallel using MPI or nVidia's CUDA. A solution should include graphical and statistical interpretation of simulation results. If we didn't make gravity a bit repulsive, you would have been able to find codes throughout the Net. In fact there is even one on every version of the BCCD (Bootable Cluster CD), which a group of us have created. You can find an ISO of it at http:/bccd.net. This would have pretty much made it a problem of finding such a program on the net and just using it. We wouldn't insult you by making such an easy problem.

-You are welcome to obtain code from the web, such as GalaxSee from the BCCD, and modify it using our modified gravitational equation.