I Matter movement versus spacetime expansion

[Robin04]

TL;DR Summary

Is the movement of matter and the expansion of spacetime experimentally distinguishable?

If I understood well, cosmology makes a difference between matter moving in spacetime and the expansion of spacetime itself. Are these concepts experimentally distinguishable, or this distinction is only in our theories?

 

[phinds]

Summary:: Is the movement of matter and the expansion of spacetime experimentally distinguishable?

If I understood well, cosmology makes a difference between matter moving in spacetime and the expansion of spacetime itself. Are these concepts experimentally distinguishable, or this distinction is only in our theories?

Yes, they are quite different. First of all, all motion is relative so when you say "Matter moving in spacetime" you have said that there is proper motion between two objects. When "space expands" (an incorrect statement at its heart) there is NO proper motion, just recession velocity. I recommend the link in my signature.

 

[PeroK]

Summary:: Is the movement of matter and the expansion of spacetime experimentally distinguishable?

If I understood well, cosmology makes a difference between matter moving in spacetime and the expansion of spacetime itself. Are these concepts experimentally distinguishable, or this distinction is only in our theories?

More generally, the difference is coordinate dependent. There are a number of threads on this.

See the posts by @Orodruin and @kimbyd in this thread:

https://www.physicsforums.com/threads/cosmological-redshift.935943/

If you measure the light from a distant object, all you have is the wavelength of the light, from which you can deduce a certain redshift. That redshift is a function of the spacetime path taken by that light from the source. Any decomposition of the redshift into this factor or that factor is coordinate dependent.

 

[Orodruin]

See the posts by @Orodruin and @kimbyd in this thread:

https://www.physicsforums.com/threads/cosmological-redshift.935943/

I remember that thread. It prompted me to write an Insight (linked at the end of the thread) that may be worth a read. Note that it is intended to be quite technical though.