"Astrophysics," Sam says. "Which is related to astronomy, yes, but different, too. My speciality is theoretical astrophysics, which studies things like stellar dynamics and evolution, large-scale structure of matter in the universe, general relativity and physical cosmology, gravitational waves, wormholes... that sort of thing." As usual when Sam's talking about anything related to the work she loves, she gets excited and tends to babble, even if she's been lecturing for the last hour and a half already.