"Duplicate" not a duplicate

Question

This question asks whether a traveler looking through a telescope will see his earthbound twin moving in slow motion. It is closed as a duplicate of this question, which asks whether a traveler moving away from earth will hear earth-originated telephone conversations in "slow motion".

It wouldn't surprise me at all if the closed question were a duplicate of something, but it's not a duplicate of the currently alleged duplicate. That's because the answer to the closed question depends on whether the traveler is moving toward or away from earth, whereas the alleged duplicate addresses only the (less interesting) case where the traveler is moving away.

So in particular, readers are told that "This question already has an answer here", and then directed to a site where the more interesting part of the question is not answered.

Again---I wouldn't be the least bit surprised if there's a real duplicate somewhere, but it would be good if readers were directed to that real duplicate.

Answer 1

As the first person who voted to close Dancing Twins as a duplicate, I think you make a valid point which is relevant generally. There is always going to be some difference between questions, or some aspect of the new question (or of both) which is not addressed in the original answers. I think the decision has to be made on the broad similarity of the central part of the question. See for example the discussions about Do black holes exist? and Is the definition of the meter arbitrary?

In the present case I think you are making a distinction which does not actually exist in the questions. Neither specifies what the relative motion of the observers is. The rocket-bound twin could be circling the Earth-bound twin; this possibility is not addressed in either case. And Electrodynamist's answer to the original makes the same points as you that what is observed depends on the relative speed and is affected by both time dilation and the Doppler effect.

Before the question was closed you were able to post an answer which addressed the issue you raised. Even if the question had been closed before you answered, you could (and can still) post a thorough answer to the original question, contrasting the two questions and covering all scenarios.

There might indeed be a better original of which this is the duplicate, but finding it takes time and effort, which mortals like us have in limited supply.