Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Iwonda on 10/12/2019 05:37:14

Title: Is everything in the universe in motion?
Post by: Iwonda on 10/12/2019 05:37:14
Is there anything in the universe that is not in motion?  The galaxies are in motion so I would assume that means everything within them is also. Is there any kind of matter in between the galaxies that is not in motion?
Title: Re: Is everything in the universe in motion?
Post by: Colin2B on 10/12/2019 08:44:09
Not in motion relative to what???
You first have to define a point which you consider to be not in motion and that is difficult.
One measurement for example shows the movement of our sun relative to the rest frame of the cosmic microwave background, but that does not assume that that rest frame is motionless.
Title: Re: Is everything in the universe in motion?
Post by: Iwonda on 12/12/2019 21:08:20
It is said that our solar system is orbiting the galaxy and the galaxies are orbiting each other.. When we look out into space it seems as if everything is stationary but that is clearly not the case.
Title: Re: Is everything in the universe in motion?
Post by: Janus on 12/12/2019 21:23:23
It is said that our solar system is orbiting the galaxy and the galaxies are orbiting each other.. When we look out into space it seems as if everything is stationary but that is clearly not the case.
The Solar system has a motion relative to the center of the galaxy. The galaxy has a motion relative to the barycenter of the local group.     If we look out at a distant galaxy, it has a motion relative to us.   The key word in all of these statements is "relative".   Motion can only be measured with respect to a reference, and that reference can be arbitrary.  When we look at that distant galaxy, and claim that it moves relative to our galaxy, we could just as easily claim that is our galaxy moving relative to it.   We generally say the former because it is the most convenient.   Thus is the case for any reference frame, we simply choose the one that is convenient for our needs.    There is no absolute reference against which we can measure motion.
Title: Re: Is everything in the universe in motion?
Post by: PmbPhy on 13/12/2019 23:34:41
Is there anything in the universe that is not in motion?  The galaxies are in motion so I would assume that means everything within them is also. Is there any kind of matter in between the galaxies that is not in motion?
Any object not subjected to non-gravitational fields are at rest in they're own frame of reference, which is an inertial frame.