MadSci Network: Astronomy

Re: Does space its self move with the movement of the galaxy?

Date: Wed Nov 25 15:49:46 1998
Posted By: Adams Douglas, Staff, R/D, Dicon Inc.
Area of science: Astronomy
ID: 911611658.As

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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