Technology and Magic
What makes science fiction science fiction, as opposed to fantasy? Both genres are speculative fiction, taking us into unfamiliar worlds. The strange worlds delight us (or appall us), and that's part of the attraction.
Roughly, the difference is this. Science fiction stories make use of ideas based in current scientific beliefs. Whatever wonders occur in the science fiction world, they should be scientifically plausible (or at least possible). But magic has no such constraint; magical creatures, persons, objects, and powers don't have to obey the laws of physics or chemistry. It's technology versus magic.
Some science fiction writers cheat. They want something in their story (faster than light travel, for instance) so they throw in some "technology" that might but probably doesn't square with physics ("warp drive" or "hyperspace"). So you can find opposing camps among the science fiction crowd, some who demand "hard" science fiction and others who grant the writer more license.
Real world scientific beliefs change over time. The speculations of one generation of sci-fi writers may lose all plausibility in the next. A hundred years ago, when Edgar Rice Burroughs wrote his John Carter books, it was scientifically plausible to imagine civilizations on Mars. John Carter's adventures may be interesting enough to pull in crowds of movie-goers, but the stories have been transformed from science fiction into fantasy by our discoveries about Mars. Technology can metamorphose into magic.
Arthur C. Clarke would agree: "Any sufficiently advanced technology is indistinguishable from magic." If a writer transported ancient Saxon warriors into modern London, the displaced warriors would see magic all around them: cars, cell phones, wondrously tall people, and so forth. (Has anyone ever tried that plot yet? It could be fun.)
In the Stargate television series, it is the twenty-first century protagonists who encounter alien technology so advanced that it seems magical. Of course, the series' writers eschew any mention of magic; the wonders we see (resurrection sarcophagi, stargates that create wormholes, etc.) are all supposed to obey the physical laws of the universe. The characters of the story often mention the technology of the Ancients (and other aliens); they don't say "magic."
The boundary between technology and magic is relative to the scientific understandings of the reader and the characters in a story. Suppose a character from our familiar world were placed in a world of limited science. He or she might be regarded as a wizard or witch . . . There's a story there, and someday I hope to write it.