Are all objects in motion? It seems like everything in the universe is in motion, at least relative to some other object.  That leads me to believe that all objects are in motion.  But how do we measure motion when we are talking about galaxies, is there any reference point that's not moving?
 A: You are correct: everything is in motion (or not) based on the reference frame. Motion is a relative concept, so you are never "moving" but only "moving with respect to something".
Find a good basic primer here: http://en.wikipedia.org/wiki/Principle_of_relativity
A: Well, all objects are in motion with respect to some other object and none of them are superior frames of reference due to Special Relativity.
Also, you may think of the expansion of the universe. Everything in the universe that is far enough is moving away from every observer in the universe in a macroscopic scale. To clarify what I mean, if an object is far enough from you, you can easily detect that it is moving away from you using redshifting and you would see that everything distant enough is moving away from you without any exceptions, although "distant enough" is dependent on some other factors.
Edit: Motion of galaxies are measured with respect to another galaxy, or if it's the rotation you're talking about it's measured with respect to the rotation axis.
A: The CMB definitely gives a preferred inertial frame at any point in the universe. However, this gets a little trickier when you include GR, and then if you are sitting in/near a deep potential well (e.g., a cluster of galaxies), the CMB may never appear isotropic, regardless of your velocity
A: But, are all inertial frames really equal? Place two objects (or reference frames if you prefer) close together, but with a high relative velocity. Do they see the same cosmic background radiation? Does the one moving relative to the other see a doplar effect in their measurements of the CMB, and in redshifts of distant objects? If the answer isn't no (i.e. we can detect velocity wrt the CMB), then there is some prefered velocity for each point in spacetime.
A: Well it can be a bit confusing.  Let's say that we have two objects that exist within the universe, and that they are in motion relative to each other. From one objects point of view, time is ticking slower than it is as seen in the "other" objects frame of reference, and there would be differences in their length measurements, etc.
Meanwhile, people say that if one of the two objects was removed, then there would no longer be motion, since motion is relative. However, not to forget, both objects were moving through time. Does that mean that once one object is removed, the remaining object suddenly stands still in time ???
So people say, "Everything is in motion (or not) based on the reference frame. Motion is a relative concept, so you are never "moving" but only "moving with respect to something".
But in the case of the two objects, both were moving across time to a certain degree, but they viewed each others motion across time as being at different magnitudes of motion. Here, in the case of the ticking of time, we do not say that one object is at rest in time and that it is the "OTHER" object that is on motion across time. Both objects are in motion across time. Thus the elimination of one object does not imply that the other object suddenly comes to a complete standstill in time.
This implies that there is a superior frame of reference of which this motion across time, for these objects, relates to.
