IMHO Sci-Fi is just Fantasy that did the math. You can add magic, but it should be grounded in some form of reality and be internally consistent. Hard SF is s

IMHO Sci-Fi is just Fantasy that did the math. You can add magic, but it should be grounded in some form of reality and be internally consistent. Hard SF is stuff that is theoretically possible but we just lack the tech for it, and especially how that might affect society. Cheap access to space is an easy example, thinking about a society with a working space elevator that enables people to live outside of traditional political systems. The similar story might be written about people stranded on an otherwise deserted island.