8 Acknowledgements
I would like to acknowledge the kind hospitality of the Aspen Center for Physics, and the anonymous
referees whose extensive knowledge of the subject has helped fill in the gaps in my understanding. Extensive
use was made of both the arXiv pre-print server and the ADS system. This work has been supported by
NASA EPSCoR grant NCCW-0058, Montana EPSCoR grant NCC5-240, NASA Cooperative Agreement
NCC5-579, and NASA APRA grant NNG04GD52G.