Stephen Hawking. Bill Gates. Elon Musk. When the world's biggest brains are lining up to warn us about something that will soon end life as we know it -- but it all sounds like a tired sci-fi trope -- what are we supposed to think?

In the last year, artificial intelligence has come under unprecedented attack. Two Nobel prize-winning scientists, a space-age entrepreneur, two founders of the personal computer industry -- one of them the richest man in the world -- have, with eerie regularity, stepped forward to warn about a time when humans will lose control of intelligent machines and be enslaved or exterminated by them. It's hard to think of a historical parallel to this outpouring of scientific angst. Big technological change has always caused unease. But when have such prominent, technologically savvy people raised such an alarm?

Their hue and cry is all the more remarkable because two of the protestors -- Bill Gates and Steve Wozniak -- helped create the modern information technology landscape in which an A.I. renaissance now appears. And one -- Stuart Russell, a co-signer of Stephen Hawking's May 2014 essay, is a leading A.I. expert. Russell co-authored its standard text, Artificial Intelligence: A Modern Approach.

Many argue we should dismiss their anxiety because the rise of superintelligent machines is decades away. Others claim their fear is baseless because we would never be so foolish as to give machines autonomy or consciousness or the ability to replicate and slip out of our control.

But what exactly are these science and industry giants up in arms about? And should we be worried too?

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