Why was it Albert Einstein -- and not some other clever physicist -- who changed our view of the cosmos in 1905? What allowed this young man to see what so many others had missed?
No one can say whether he was truly the smartest man alive. There certainly were other smart scientists at work at the same time, but Einstein did have a unique vision, a gift for identifying the most important problems in physics, and a dogged determination to keep pursuing them.
One advantage -- and it certainly wouldn't have seemed like an advantage at the time -- is that Einstein was an outcast.
By 1905, though 26, he had not yet earned his doctorate, and was not entrenched in the ideas of the physics ''establishment." He had been reading the latest papers, and understood the key ideas but he had nothing invested in the physics ''status quo." In other words, he had nothing to lose.
''He comes in entirely as an outsider," said Harvard historian Gerald Holton, a noted Einstein scholar. ''He lets his mind wander. He's not endangering his academic position because he doesn't have one, and he can take those risks."
Einstein also had a gift for discerning the ''big picture," allowing him to grasp hidden truths and, when necessary, to abandon cherished ideas.
While other scientists were metaphorically climbing the north face of Mount Everest, Holton said, Einstein realized that ''it's the wrong mountain and it's the wrong face, and you ought to really be hovering above it all."
And, of course, Einstein was incredibly intelligent -- ''brighter than anyone else in the world at that time," according to Michael Shara, a curator at the Museum of Natural History in New York who coordinated a major Einstein exhibit that continues to travel the country. ''Maybe brighter than any scientist who had ever lived until then."
Einstein's environment likely bolstered his creativity in the years leading up to the 1905 ''miracle" -- especially following his move to Bern, Switzerland, in 1902. His school years, and the first years after graduation, had been full of frustration: Classes demanded rote memorization; his science teachers seemed uninterested in the most recent developments. After graduation, he struggled to find work.
But his fortunes improved after landing an entry-level job as a technical examiner at a government patent office there. .
In hindsight, the patent office job seems ''beneath" the Person of the Century -- but it might have been exactly what he needed. It forced him to think visually, to read complicated diagrams, and assess their merit. Many of the proposed devices involved the synchronization of electronic clocks, a task that Harvard historian Peter Galison believes may have pushed Einstein toward a new understanding of space and time.
At the very least, the patent work left Einstein's evenings free to discuss physics and philosophy with a close circle of friends, secure in the stability of his job and in the support of a loving wife, his former classmate whom he had recently married.
''Here, for the first time, he had no financial burden on his young shoulders," Ruth Aegler said as she led a recent tour around the former Einstein apartment in Bern, now a museum. ''He was so happy. He was in love. He had a child. He had a good job. Everything in his life was settled, satisfied."
While spring 1905 marked the blossoming of Einstein's ideas, it almost certainly did not mark their germination. By the time his paper on special relativity appeared, Einstein had spent the better part of a decade reading the latest scientific literature -- as well as the philosophical works of David Hume and Ernst Mach -- and contemplating the nature of the physical world.
''I think by [his] late teen years, and the early 20s, he really was immersed in thinking about space and time," Shara said. ''This was not someone who would idly consider this interesting problem for five or 10 minutes, or perhaps blab about it for an hour over a cup of coffee. This was someone who for nearly 10 years really thought of little else."
Einstein himself, later speculating on the roots of his great intellectual leap, dismissed any notion that he was somehow ''destined" to solve the riddle of relativity.
''I know perfectly well that I myself have no special talents," he wrote. ''It was curiosity, obsession, and sheer perseverance that brought me to my ideas."