Simplify the following text for a Grade 8 native English-speaking person.
Original: In the late '70s , Phelps and one of his former students , Roman Frydman , conducted some research on the implications of assuming rational expectations , first independently and then in collaboration .
Simplified: In the late '70s , Professor Phelps researched with Roman Frydman , who was taught by Phelps . They worked on rational expectations and showed problems in it .