Johnny Depp undergoes an existential file transfer in "Transcendence."Warner Brothers

Science fiction doesn't exist in a vacuum. Well, sometimes it does -- in deep-space scenes -- but culturally speaking, science fiction almost always proceeds from real science and/or cultural concerns. One of the enduring pleasures of being a sci-fi nerd is tracking how science fiction constantly holds up a funhouse mirror to the real world.

This is especially true at the movies, where science fiction has a rich history -- going back more than 100 years now -- of projecting our hopes and fears onto the big screen. Nuclear war. Space travel. Robot revolution. Those sorts of things.

The much-anticipated sci-fi thriller "Transcendence," starring Johnny Depp and opening Friday in theaters, is squarely in the tradition of such notional sci-fi. The film deals directly with the concept of mind uploading -- sometimes called whole brain emulation (WBE) -- in which the human brain is digitized and transferred to a computer, ushering in a new era of posthuman immortality. We take a look at "Transcendence" and the science behind the fiction.

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Ever get that feeling someone is watching you? Johnny Depp as Dr. Will Caster in "Transcendence."Warner Brothers

"Transcendence" tells the story of Dr. Will Caster (Johnny Depp), the world's foremost expert in the field of Artificial Intelligence. Caster is on the brink of assembling a self-aware supercomputer dubbed PINN (Physically Independent Neural Network). The breakthrough concept of PINN? The computer will not only have instant access to all of the world's collective knowledge, but will have a replicated neural system allowing it to think, feel and react like a human being.

Things go sideways, however, when Caster is targeted by a radical anti-technology terrorist group. Dying from the effects of a radioactive bullet, Caster arranges to have his own mind uploaded into PINN before he physically dies. Merging with the supercomputer, Caster becomes potentially omniscient and immortal.

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Nice place! Co-stars Morgan Freeman, Cillian Murphy and Rebecca Hall meet with the new and virtual Johnny Depp.Warner Brothers

The idea of Artificial Intelligence run amok has, of course, been a staple in science fiction movies for decades -- from HAL 9000 to "Her." In "Transcendence," the PINN entity is already self-aware and capable of learning, planning and taking action in the real world to accomplish its goals.

In the realm of contemporary AI theory, that would place PINN in the category of AGI (Artificial General Intelligence) or "strong AI." These designations are used to indicate artificial intelligence that is equal to (or greater than) the intelligence of an average human being -- a machine that is conscious, self-aware and autonomous. For now AGI is only theoretical, but proponents of the technological singularity hypothesis predict the reality is anywhere from 15 to 30 years away.

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Separate but related to the idea of AGI, the concept of mind uploading proposes a kind of a shortcut to the goal of a self-aware, sentient machine: Just upload a real brain in there. When the fast-fading Dr. Caster realizes the end is near, he essentially digitizes the entirety of his own mind -- thoughts, feelings, memories -- and performs a kind of high-tech existential file conversion.

As a sci-fi thriller, "Transcendence" necessarily takes liberties with the science and presupposes a level of technology we haven't yet achieved. Mind uploading is still entirely hypothetical and would require significant breakthroughs in dozens of disciplines. First off: Scanning and mapping the brain's 86 billion neurons on an atomic, and perhaps even subatomic, level.

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Brain Replication Isn't CheapCorbis

After that comes the real work: Inputting the data to an artificial neural network and creating a new entity -- sometimes called a "personality construct" or "infomorph" -- indistinguishable from the original mind. "Transcendence" employs plenty of modern technological details to update the concept, but the essentials of man-to-machine mind transfer have been batted around in sci-fi stories from Asimov to "Avatar."

In the real world, several research initiatives have claimed to replicate at least some parts of animal brains -- rats and worms are popular. Last year, the Human Brain Project was awarded $1.3 billion by the European Commission to model a human brain in silicon. If you're doing the math at home, that's one-and-half cents per neuron.

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Kate Mara (left) leads an anti-technology extremist group in "Transcendence."Warner Brothers

The inherent weirdness of sentient AIs and mind transfer drives the story of "Transcendence," but like many science fiction movies, the film features plenty of scary and fascinating elements in the corners of the frame. For instance, the terrorist group that guns down Dr. Caster employs the unwieldy acronym RIFT -- Revolutionary Independence From Technology. In the film, RIFT is an extremist organization dedicated to the motto "Evolution without Technology."

As such, the group is clearly associated with the movement sometimes called New Luddism, often affiliated with causes such as anti-globalization and progressive environmentalism. While it's important to note that most organizations in this arena are avowedly non-violent, there have been recent instances of neo-Luddite terrorism. Ted Kaczynski, also known as the Unabomber, infamously espoused anti-technology ideas. A string of mailbomb attacks in 2010-2012 -- targeting scientists in Italy, Mexico and Sweden -- is believed to be the work of a loose coalition of anti-technology groups.

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But perhaps the most disturbing passages in "Transcendence," from a strictly visceral point of view, are the images of Dr. Caster dying slowly and painfully after getting shot by the RIFT terrorists. In the film, the deadly bullet has been treated with radioactive polonium, as a kind of grisly insurance policy in case the initial shooting didn't do the job.

The incident is clearly meant to reference the death of Alexander Litvinenko, the former Russian security officer who was poisoned in 2006 with the highly radioactive element polonium-210. No charges were ever brought in the murder, but it's widely believed that Litvinenko was assassinated by Russian spies who dosed Litvinenko's tea with polonium.

Radioactive bullets are indeed a reality, but not quite as depicted in the film. Depleted uranium bullets are used by several military forces worldwide as armor piercing ammunition, due to the material's extreme density. Uranium rounds don't pose the same radiological danger as polonium, but they're still a hazard. Specifics can be found at The International Coalition to Ban Uranium Weapons.