Hard science fiction treats physical law as a constraint, not set dressing. The story obeys what we know about gravity, light, biology, and computation, or it invents rules and then keeps them. Soft science fiction borrows the vocabulary (warp drives, telepathy, the Force) and spends its energy elsewhere. Both can be great.
The Canon shows the range. 2001: A Space Odyssey got vacuum silence and centrifugal gravity right before the science was cheap to look up. The Martian solves survival one chemistry problem at a time. Interstellar rendered its black hole from Kip Thorne's relativity equations. Primer treats time travel as an engineering project and refuses to simplify the consequences. Arrival turns first contact into a linguistics problem. Gattaca asks what a genome really decides. Ex Machina runs a Turing test and means it.
Every film carries a Hardness rating, zero to five stars, our read on how seriously it takes its own physics. That is why 2001 and Primer sit near the top while Star Wars sits far below and still earns a spot. The label is broad here: thoughtful sci-fi worth your evening, with the genre fidelity stated up front so you know what you are getting before you press play.
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