: fiction dealing principally with the impact of actual or imagined science on society or individuals or having a scientific factor as an essential orienting component
Even a limiting dictionary definition is still hugely broad.
The sci-fi part can be considered the outer shell, or casing, on top of the real story in many instances.
A lot of sci-fi flicks are nothing more than remakes of older stories/films... but in space! A most blatant example is the 90's remake of "Lifeboat"; originally a Hitchcock b/w suspense film. You could take "Lifeboat" and make it work in any genre or time period. You can do that to any film, actually. In this case, it's sci-fi at its shallowest. Just trading backgrounds... in space!
Other shows, such as "The Invaders" from the 60's, are sci-fi... but you're not going to see a lot of pseudo-science or flying saucers about. One man knows for sure that aliens are slowly taking over the planet... but noone believes him. To make matters worse, the "aliens" look suspiciously identical to human beings, so who can he trust? With a formulaic pattern of moving to a new town each week (a la "Fugitive") he tries to sound the alarm and prove his claim.
"Invasion of the Body Snatchers" - classic sci-fi about seed-pods from outer-space replacing humans one by one. Except the film's not really about the dangers of being absorbed by plants that come from beyond. This is another great example of using sci-fi (and horror, also) as a "wrapper" around a totally different topic.
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The best part of that definition is "or
imagined science".
There's no stopping you there, if you want to really go to town. Scientist discovers that Newton was wrong. Part-time inventor makes a time-machine. Astronomer notices that the sun is about to go nova. You can come up with almost anything, in sci-fi, and noone's going to really question it.
Michael Crichton made his fortune by making up crazy half-assed scientific theories as devices in his stories... entertaining for sure, integral to the plot... but still something that he just whipped up one day after some
, I bet.
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(not quite done)