For context there is a graduate student who has graduate from my program (at my school) working in my subfield (high energy theoretical physics) but he graduated before I joined the program so I never got to introduce myself.
He's now a post-doc at a highly respected university and is probably extremely busy.
However, I would really like to reach out to him and ask him for some advice for a beginner in the field, (I'm just starting my second year of the PhD program). Do you think it is appropriate to cold-email him and ask for some advice or the opportunity to speak with him over skype or on the phone or some form of communication?
I feel a little bad because I never introduced myself and I'm really scared of being flat out rejected by him but I also feel that he might have some really good advice for me.
Mostly, I'm worried about how to write the email and how I might sound (desperate?) to them.