First some context: I'm a Ph.D. student in Physics. I have been discussing with my supervisor the objectives for the Ph.D. project and we have been looking at some papers from the field.
In that case, recently I've come across a quite interesting paper, one of the authors being a very renowned researcher in the field. The paper raised a conjecture and pointed out that one what was necessary to follow that line of investigation in order to prove or disprove the conjecture. I got quite interested in pursuing this objective and my supervisor considered it to be a good idea for the project.
It so happens that a few days after, I have found a paper by another author, which is also a quite renowned researcher, briefly disputing the claims made in the first paper.
Given my current knowledge, I would consider that the authors of the first paper are correct, but of course I might be wrong.
Now, the first paper is three years old and the authors didn't revisit the issue in another publication.
I considered the possibility of contacting the corresponding author and asking about the comments made in that response paper. In particular I would like to ask if they changed their view on the problem after all or if I'm correct in my conclusions and they still believe in their first proposition.
Also I considered asking if he still views that as a line of investigation worth pursuing.
Are that kind of questions considered ok or are they viewed as unethical? My worries are: (1) if I can indeed ask for his views on that brief response and if it made then revisit their positions and (2) if it is ok to ask if he considers a good idea to pursue this objective.