Increasing the number of authors in the research article after uploading it on arxiv I have done some work and want to upload that research work on Arxiv. The problem is that the second author wants to work more on this and doesn't want to upload the result to Arxiv. I am thinking that I will upload the result on Arxiv and then I will keep doing research on that thing, so if get more results, then along with the second author I will submit the result to a conference.

Question: Suppose I upload an article on Arxiv as a single author and after that I work on the same problem and get some results. Will it be possible to submit again the additional result with two authors on Arxiv and to a conference? Is there any problem with the process I have described above?
I imagine that there is no problem from the side of arXiv: submissions there are versioned, so you can always update a preprint there. arXiv also explicitly allows you to submit the same work to a different venue later on.

The problem with your process is that you do not seem to have a trust relationship with your second author. If your second author does not want your joint paper uploaded to arXiv and (i) you do it anyway, and (ii) do not even make him an author even though he was part of the research, then what does this say about the relationship the two of you already have? And what does it say about the kind of relationship you hope to have with him in the future? If I were that second author, I would consider uploading a joint paper over my objections a major breach of trust. I would not ever want to work with you again.