QUESTION:
Earlier, we asked a question: "Why do planets spin, and why do planets move 
in orbits?"  In the reply, it was stated that, "Almost nothing in 
the Universe is sitting in space absolutely still."  We wonder, 
"Is there is anything known that is absolutely still in space?"

ANSWER from Howard Bushouse on April 29, 1996:
Hmmm, that's a good question. I probably should have said in my
original response that nothing (as opposed to almost nothing) is
sitting absolutely still in space. The problem is that when we
say something is "sitting still", we mean that it has no motion
relative to some other object used as a reference. For example,
when you are sitting still, it means that you aren't moving relative
to the chair you're sitting in, or the room that the chair is in.
Yet if you look at the bigger picture, we're all constantly in
motion as we get carried along by the earth in its orbit in space.
Similarly, the sun around which the earth is orbiting is itself
orbiting around the center of our Milky Way galaxy. And our galaxy
is moving around relative to other galaxys in our local group of
galaxies, and the local group is moving ...

So you see, in space all motion is in relation to something else
used as a comparison. So in order for something to be sitting still
in space it would have to be motionless relative to some absolute
reference. And what do you use as the absolute reference?