The redshift from recession or expansion

[micomaco86572]

Almost all textbooks tell us that the cosmic redshift is arised from the cosmic expansion rather than the recession of the celestial objects. I think the conclusion is basically based on the assumption of Copernican Principle, i.e. there is no favored position in the whole universe. But what if we give up this assumption? Can we still lead to the conclusion that the redshift is caused by expansion?

thx.

 

[Chalnoth]

Almost all textbooks tell us that the cosmic redshift is arised from the cosmic expansion rather than the recession of the celestial objects. I think the conclusion is basically based on the assumption of Copernican Principle, i.e. there is no favored position in the whole universe. But what if we give up this assumption? Can we still lead to the conclusion that the redshift is caused by expansion?

thx.

It's largely just a matter of the description of reality rather than actually being a physical discrepancy. If you so choose, you can select a different coordinate system where the expansion appears to be primarily due to the recession instead of the expansion. The math is just easier in the coordinate system where the expansion is the cause of the redshift.

 

[micomaco86572]

It's largely just a matter of the description of reality rather than actually being a physical discrepancy. If you so choose, you can select a different coordinate system where the expansion appears to be primarily due to the recession instead of the expansion. The math is just easier in the coordinate system where the expansion is the cause of the redshift.

Thank u, Chalnoth. I understand it, now.

 

[Naty1]

lots more detail here:
https://www.physicsforums.com/showthread.php?t=522587

 

[sardar]

I appreciate your curiosity and critical thinking about the concept of redshift. However, it is important to note that the conclusion that redshift is caused by cosmic expansion is not solely based on the Copernican Principle. There is a wealth of evidence from various observations and experiments that support this conclusion.

Firstly, the discovery of the cosmic microwave background radiation and its uniformity in all directions strongly supports the idea that the universe is expanding uniformly, as predicted by the theory of cosmic expansion. This is not just based on the Copernican Principle, but also on the principles of isotropy and homogeneity in the universe.

Additionally, the measurements of the redshift of distant galaxies and their recession velocities, as determined by the Hubble constant, also provide evidence for cosmic expansion. This is not just a coincidence or a result of the Copernican Principle, but a direct consequence of the fundamental principles of physics, such as the equations of general relativity.

Furthermore, the observed relationship between the redshift and distance of galaxies, known as the Hubble's law, also supports the idea of cosmic expansion. This relationship has been tested and confirmed by numerous studies, and it is not dependent on the Copernican Principle.

In conclusion, while the Copernican Principle is an important concept in our understanding of the universe, it is not the only basis for the conclusion that redshift is caused by cosmic expansion. The evidence from various observations and experiments strongly supports this idea, and it is widely accepted in the scientific community. Giving up the Copernican Principle would not change this conclusion.