Complex sentence: When Cooper and Amelia return to "Endurance", 23 years have passed on Earth due to gravitational time dilation, and the adult Murphy now works for NASA, helping Brand solve his gravity equation.
Split into simpler sentences: When Cooper and Amelia return to "Endurance", 23 years have passed on Earth due to gravitational time dilation. The now adult Murphy is employed by NASA, helping Brand solve his gravity equation.