I just watched a show on dark matter on a cable channel. I think the formula they are using to figure out dark matter's existence is flawed. If you add up the mass of our planet, moon, soar system ect.., they say there shouldn't be enough gravity to hold in the outer systems in our galaxy. I think their error lies in that statement. Let's say we have a 5lb. block at our house. That block weighs 5lbs. not only from its mass alone. In reality it has more weight than 5lbs. at rest at the same given gravity. The formula for the mass of that object should take in to account centrifugal force of an object traveling +/-1035mph on a radius of +/-3963 miles. I'm not good at the math part, so I'll leave that to someone smarter than me. You would have to figure out how much force is exerted throughout the entire earth, figure out the displacement of measurable mass, then add that to the mass of earth. This way the true mass of the earth can be calculated at rest. If you take this in to account, I'll bet that the discrepancy disappears.