Some things have to be seen to be believed. Others have to be believed before they can be seen.
Sometimes the most interesting and useful inventions don't come from the minds of scientists, but from the minds of fiction writers who create entire universes, as well as the things that exist within them.
Writers have dreamed up ways to make the impossible possible, often defying the laws of science and pushing the bounds of reality.
While we're nowhere near being taken over by the clone armies of "Star Wars," other ideas that were created by science fiction's dreamweavers have found their way into our world.
FOXNews.com takes a look at some of real-life things that were "invented" first by science fiction's finest.
1. Cell Phones
Beam me up, Scotty! Long before cell phones became a must-have accessory for everyone from middle schoolers to CEOs, one science-fiction television show had its characters talking across galaxies on hand-held wireless communication devices.
The "communicators" that Capt. James T. Kirk used to talk to the crew of the Starship Enterprise on "Star Trek" influenced cell-phone inventor Martin Cooper, who said he was inspired by the flip-cover devices as he was developing mobile-phone technology at Motorola.
On April 3, 1973, while going boldly where no man had gone before (well, he actually was walking down a New York City street), Cooper placed the first handheld cell-phone call — the handset weighed more than two pounds — to Joel Engel, his rival and head of research at Bell Labs.
Considered the father of science fiction, 19th-century author Julies Verne was an inspiration to the pioneers of undersea travel when his 1870 novel "Twenty Thousand Leagues Under the Sea" gave the world Captain Nemo's Nautilus and a glimpse at what submarines could be.
Primitive hand-cranked submarines had been created — and even used in war — before Verne's novel was published, but it was his vision that spurred innovation of the modern, mechanical sub.
The Nautilus, about 230 feet long and powered by electricity generated using the sodium in ocean water, was more akin to today's submarines than to the small human-powered ships of Verne's time. It also had a galley kitchen, a library and a pipe organ.
The world "robot" was first used in 1921 in Czech writer Karel Capek's play, R.U.R. (Rossum's Universal Robots), and comes from the Czech word "robota," meaning "forced labor," according to the Oxford English Dictionary.
Parts of the play take place in a factory that makes artificial people. Created to work for humans, the robots eventually rebel, leading to the end of the human race.
Isaac Asimov coined the term "robotics," and his 1942 short story "Runaround" listed the Three Laws of Robotics, Asimov's rules that robots must obey.
In order of priority: Robots must not hurt humans or allow them to be hurt. Robots must obey humans, unless that conflicts with the first law. Robots must protect themselves, unless that interferes with the first or second law.
Films such as "Blade Runner," "2001: A Space Odyssey" and "Terminator," and television shows like "Battlestar Galactica" show what happens when robots break the laws and run amok.
It's usually some combination of chaos and destruction, but so far the most advanced robots -- like the latest model from Japan that strolls down the catwalks of the fashion world -- have yet to rebel.
4. Space Travel
Long before Yuri Gagarin left our atmosphere behind and Neil Armstrong set foot on the moon, science-fiction writers imagined ways that human beings would break free from the confines of boring old Earth and take to the stars — or at least to the moon.
In fact, in novels and in film, man was visiting the moon years before Wilbur and Orville Wright were able to get an airplane off the ground.
Jules Verne published "From the Earth to the Moon" in 1865. In 1901, H.G. Wells' "The First Men in the Moon" was published, and the two inspired the first science fiction film, Georges Melies' "A Trip to the Moon."
In the 14-minute film, made in 1902, six astronomers build a bullet-shaped ship and shoot themselves to the moon — out of a cannon. In the film the moon watches the ship approach, hitting it straight in the eye.
And what did the first men on the moon do when they landed? They took a nap, of course.
5. Home Entertainment Systems
Televisions were still black-and-white behemoths in 1953 when Ray Bradbury wrote "Fahrenheit 451." But his world, in which books are banned and people watch "parlor walls," presaged a society in which television dominated.
The big-screened sci-fi entertainment systems of his dystopian novel have found their way into real-life homes across America, with digital home theater systems, media servers and video game systems played on giant plasma and LCD screens.
Even though he foresaw the color TV panels of the future, Bradbury told L.A. Weekly in 2007 — after being awarded the first Pulitzer Prize given to a science-fiction writer — that his novel reflected his fear that TV would kill interest in reading and literature.
"They stuff you with so much useless information, you feel full," he said.
However, noted the article, "he says this while sitting in a room dominated by a gigantic flat-panel television broadcasting the Fox News Channel, muted, factoids crawling across the bottom of the screen."