- A wal
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The actual cause of gravity.
This has to do with the special theory of relativity. http://www.physicsforums.com/blog.php?b=743 See below for a nutshell description. Length contraction and time dilation work slightly differently with angular velocity than they do with linia velocity. They get curved and accumulate to produce gravity. It's the orbit of the electrons that create the time dilation and length contraction associated with gravity, but it's really just an extension of special relativity.
Basically if an object is floating in space and it sees another object coming towards it at half the speed of light then it could just as easily claim that it's moving towards the other object at half the speed of light and the other object is stationary. There is no way to tell which one is moving. The only statement you can make is that they moving towards each other at half the speed of light. All the laws of physics remain the same in any inertial frame, meaning all frames are equal and no frame can be said to be unique in any way. Having said that, you could use the cosmic background radiation as a frame of reference for all others, but you could do that with any frame of reference. When you're sitting on a train and you throw a ball into the air it does go flying backwards, because the laws in all non accelerating frames are the same, including the speed of light. You can't measure your speed relative to light because you'll always get the same answer. That means if two objects are heading away from Earth at different relative velocities and you shine a flash light, the light beam will pass both of them at the same speed, meaning all three observers measure time and space differently to keep the speed of light the same. Velocity is just a measurement of distance over time. There's one spacial dimension involved because you can always draw a straight line between any two objects, and time. Both shorten from the perspective of an accelerating observer to keep the speed of light constant. Simple.