Uplift your physics Brin.

I recently became interested in the author David Brin who is famous for writting the two uplift trilogies. The books deal with species uplifting other close to sapient species to the point where they can create civilization and starships and the works. The only species never to have been uplifted are humans who speculate they may have been and that the answer lies in the core of the sun. Everything takes place in the five galaxies (five galaxies)and there is communication between many different races. David Brin is considered a hard SF writer but it occured to me he uses many cheats.For one there is FTL travel otherwise cross galaxy travel would be impractical and every single planet they go to has an oxygen atmosphere. How is this hard? What makes up for these two facts? I plan to find by reading Startide Rising his supposes magnum opus... But well see.