Astronomy is such a small world that it can be a little unsettling at times. In Princeton's astro department, there is a tradition where the grad students invite a professor or notable person to come for lunch on Thursdays, imaginatively known as 'thunch'. This stemmed from the Tuesday faculty lunch at the Institute of Advanced Studies (IAS) in Princeton, where following morning seminars the grad students are barred from joining the faculty members for lunch. In the 70s, some grad students here decided to introduce thunch, whereby only people without PhDs are allowed in apart from the guest.

Generally, the guests are distinguished visiting professors either at Princeton University or the IAS, but occasionally we get some famous names, like John Nash and Freeman Dyson.

In the past couple of weeks however, we have had the interesting experience of hosting thunch for guests who were ex-grad students here. Both of them, David Weinberg of Ohio State and Nick Gnedin of Fermilab, were students in the 80s and 90s, so they've had the same experience of attending thunch. I spoke to David Weinberg and told him briefly about my project on measuring the topology of cosmological reionisation. As I started to explain the method I'm using to measure the topology, he (politely) interrupted me and said, 'Yes, I know about that. I worked on that when I was a grad student'. I then realised that the main paper which described the methodology I'm using is Gott, Weinberg and Melott 1987. Rich Gott is still on the faculty here and I guessed prior to this that Weinberg must have been a grad student at the time, but I didn't really make the conscious connection between the student who had worked on the paper and the middle-aged professor at thunch until he told me.

Even more surreally, that paper which I'm using now was based on David Weinberg's very first semester in his first year as a grad student. It's funny how his first year project has spanned a couple of decades to become an integral part of MY first year project. I can only hope that my own semester projects will eventually have some longevity.