Webster's English Dictionary defines hard science fiction as being 'characterized by an emphasis on scientific accuracy or technical detail or both' (just kidding it's Wikipedia). So, basically sci-fi that would satisfy 'Comic Book Guy' from The Simpsons.
Sick of sci-fi blockbusters with big-budgets and no brain? Then look no further than this collection of modern indie masterpieces guaranteed to make you ponder time, space, and everything in between. At least a couple gems you've never heard of guaranteed!
Movies in the vein of Interstellar: These cerebral sci-fi masterpieces are guaranteed to get you thinking about time, space, destiny, free-will, and pretty much every other insoluble existential mystery. The thinking man's blockbusters!
Movies in the vein of 'Gravity': tense space-based thrillers in which one of the manifold things that can go wrong on a space mission inevitably does, leaving the crew stranded and understandably a bit miffed at Houston.