I think it has something to do with a sense of shared experience among the grad students. Like I wrote previously, the grad students in my department aren't very close. Even within my lab, we're all working on different projects so there isn't much collaboration (unfortunately, some interpersonal conflicts among lab members have also kept us from bonding as a group). I do my best to help other students who ask me for help no matter what my experience with their project, but I still don't have a sense of really going through this with anyone else. I'm really doing my own thing here, and suddenly this makes me very sad. Have I imagined this isolation, created or exacerbated it?
After considerable reflection, I think the answers are no, no, and no, but I haven't always felt so disconnected. My first year I had a few classes with a set of people and I tried very hard to invite everyone to parties (Jon and I hosted 3 in our first 6 months here) but realized before the end of that year that not even my cohort was a cohesive group. When I was in the midst of my interdisciplinary project, I had those other students to bond with, but now most of them are in different places. I was actively involved in two different efforts to create student-led activities for grad students in the department, but neither really caught on and are defunct. As I also mentioned previously, I think this pattern of increasing isolation in the later stages of grad school is pervasive in my department. I've got to try to do something about it. More thoughts on this soon.