From that link I posted. An animated effect of the process.http://en.wikipedia.org/wiki/C enter_of_mass
This is a rather well documented and principle of physics. It is also why modern math based physics is fucked up, which I have pointed out innumerable times.
This works on the molecular to galactic to universal scale.
Trillions of galaxies? Even more stars. Even more dust and plasma. All swirling around in motion, tugging on each other.
For instance, Earth has a gravity relationship to the sun, and another to Jupiter, but its relationship to the both of them is in another direction, one which changes according to orbital positions. Now add the rest of the celestial bodies and components in the solar system, galaxy, and rest of the universe and those individual relationships combines with those barycentric relationships that are constantly moving and changing and you have one hairy bunch of gravity and energy relationships to keep track of. Which there is no possible way physicists and cosmologists could have done in making their pronouncements that Topix atheists take as the Gospel truth in the belief they are glorified stellar shit.
Ask just where and how they have come up with these totals for the universe that they use in their determinations. You have all of that motion and we haven't even seen it all yet.
Like I said, this happens from the atomic scale to the universal scale. You just don't have that flat fixed relationships crap they try to bedazzle you with. This is vibrational stuff. Not a damned part of it static.
The universe is a quivering mass, and we are part of it. Think.