Consider the following chain of questions, presented in chronological order:
- Redshifting of Light and the expansion of the universe
- Have red shifted photons lost energy and where did it go?
- Do photons lose energy due to gravitational redshift? If so, where does the lost energy go?
- Redshift due to a static gravitational field and the conservation of energy
The second was marked a duplicate of the first, and the third a duplicate of the second. Now the fourth is being voted closed as a duplicate of the third.
I agree the fourth is a duplicate of the third, as both ask about gravitational redshift. The first, however, asks about cosmological redshift. These are quite different, and indeed the asker for the latest questions points out that the cries of "Noether doesn't apply" in response to the earliest question are just wrong in this newest context.
The link is the second question, and to be honest I don't know whether it is about gravitational or cosmological redshift.
This seems to be a general flaw in the system, but I'm not sure what the fix is. Two options come to mind:
- Just ignore this condition. If we close A as a duplicate of B and B as a duplicate of C, then even if A is not really a duplicate of C, they'll be related enough that the person can piece together an answer on their own. Besides, B usually accumulated B-specific answers before being closed, and these probably answer A.
- Restrict ourselves to only marking exact duplicates (in concept if not in words). (I feel the word "exact" used to be here in this context, but I can no longer find it.) I have anecdotally noticed over the years that as we experienced users see more and more questions, we are more likely to see similarities to other questions, and are perhaps a bit quick with declaring questions to be duplicates.
What do people think? Is there something wrong here? What can we do to fix it? See also Liberal definition of duplicate questions and the health of physics stack exchange.