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The Big Bang theory is the idea that the entire universe began as a pinprick that has been expanding ever since—essentially, that the only reason the universe feels so vast is because it's had 13.8 billion years to get that way. The idea itself has held up pretty well, although scientists still aren't quite sure what force is driving all that growth.And of course, the theory itself doesn't do anything to explain where precisely that first dot of the universe came from in the first place, hence the brainteaser. And we do mean it when we say brainteaser—Hawking's explanation includes this excellent line: "Ordinary real time is replaced by imaginary time, which behaves like a fourth direction of space."But don't let that scare you off; his main point is surprisingly easy to grasp: Hawking approaches the problem by offering a detailed analogy, comparing space-time to any other continuous, curved surface, like the surface of the Earth. "There is nothing south of the South Pole," Hawking says. The same principle holds with the universe: "There was nothing around before the Big Bang."Watch the full response õ
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