The discussion centers on the distinction between matter movement in spacetime and the expansion of spacetime itself, exploring whether these concepts can be experimentally distinguished or if they are merely theoretical distinctions.
Participants express differing views on whether the concepts of matter movement and spacetime expansion can be experimentally distinguished, indicating that the discussion remains unresolved.
The discussion highlights the complexity of the concepts involved, including the potential limitations of definitions and the dependence on coordinate systems in interpreting redshift.
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.Robin04 said: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?
Robin04 said: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?
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.PeroK said:See the posts by @Orodruin and @kimbyd in this thread:
https://www.physicsforums.com/threads/cosmological-redshift.935943/