This isn't a book, but I think any Star Wars fan would love the radio drama of A New Hope from back in the 80s. It fills in Luke's backstory and adds a lot of detail that the movie couldn't explain. You get to meet Biggs Darklighter! Great fun, very worthwhile listening (terrific for the car!). Some of the original actors play the parts (Luke, C3PO).
Agree with checking out some of the Golden Age authors such as Asimov and (juvenile) Heinlein. The library will have lots of those for him to try and he can see what appeals. I'm not sure about Dune, but who knows. Has he already read the Wrinkle in Time books? How about Jules Verne? Although written in another language more than 100 years ago, they hold up surprisingly well. Again, there are some great audio versions of Jules Verne's work out there, too.
Is he only into hard science fiction or does he like fantasy at all? There's always The Earthsea Trilogy by Ursula LeGuin. Most anything by Diana Wynne Jones (such as Howl's Moving Castle, Chronicles of Chrestomanci, Dogsbody, and so much more) is great.
For a book listed as a "fantasy/physics/metaphysics tale" he could try The Keeper series by Ted Sanders (NOT to be confused with another, very adult, series called The Keepers by Donna Augustine, no, no, no). Now, I haven't read any of these books yet, but have heard very good things about them from folks I trust.
Best wishes!