|MadSci Network: Astronomy|
Very interesting question, Gerald. First of all, Einstein showed that there is no preferred reference frame in spacetime. That is, there is no absolute reference frame that we can measure the motion of points in spacetime relative to--we can only measure relative to other points. When you say there's something you "don't know what to call it", you're right, because there isn't anything we can measure the movement of the universe, or anything in the universe, against. We can simply decide whatever unaccelerated reference frame we wish to measure against appropriate for any particular problem. That said, let's look at whether space itself can move relative to a chosen reference frame. It can. Near a spinning Black Hole, for example, the tremendous mass of the rotating hole can cause what is called the "dragging" of inertial frames. This means, essentially, that spacetime itself is being twisted by the spinning hole. A spaceship falling into the hole would move sideways a bit as viewed by a distant observer who was stationary relative to the hole. But an observer on the spaceship would detect no apparent sideways motion because the spaceship would be simply falling the shortest path through the space being dragged by the spinning hole. I know this stuff is a little difficult to grasp, but I hope that helps clear up some of your question. As to what reference frame to choose when programming a time machine, I'm afraid I can't answer that one without looking at the manual for the machine in question. If you have one, I'd be very happy to examine it for you. Best wishes, Adams Douglas Senior Developer Dicon R&D
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