Hi Jeff,
A lot of scientists understanding of the cosmos is based on mathematical elegance, and conjecture. Some things, like the aftermath of the Big Bang, can be measured. Gravity can be measured, but the source of this weak force has had scientists stumped. Using a theoretical parallel universe model, gravity makes sense. It ties neatly into other space/time theories too.
NOVA has been running a series on it all:
http://www.pbs.org/wgbh/nova/elegant/program.html