At present, I can be most practically reached via email.
My university email is
rtrosten AT andrew DOT cmu DOT edu,
and my personal email is
rct10 AT outlook DOT com.
I tend to respond quicker on the university email, but feel free to send to whichever one makes more sense for your inquiry.
If you'd like some worse methods of contacting me, consider the following, in decreasing order of practicality:
Snail mail. Generally a decent idea, assuming you have my mailing address; you just need to rely on the post.
Telegram. I do know Morse code so it wouldn't be the end of the world, but I have no idea where to go to even receive such a thing.
Slingshot with a note attached to the rock. You'd need to aim high, as I live near the top floor of my building.
Carrier pigeon. I don't know where you are, so please make sure the pigeon knows how to get back home by itself.
Summoning circle. Too many resources for a very low chance of success – but who knows, maybe this time it'll work!