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JUST about a hundred years ago, Albert Einstein began writing a paper that secured his place in the pantheon of humankind's greatest thinkers. With his discovery of special relativity, Einstein upended the familiar, thousands-year-old conception of space and time. To be sure, even a century later, not everyone has fully embraced Einstein's discovery. Nevertheless, say "Einstein" and most everyone thinks "relativity."

What is less widely appreciated, however, is that physicists call 1905 Einstein's "miracle year" not because of the discovery of relativity alone, but because in that year Einstein achieved the unimaginable, writing four papers that each resulted in deep and formative changes to our understanding of the universe. One of these papers - not on relativity - garnered him the 1921 Nobel Prize in physics. It also began a transformation in physics that Einstein found so disquieting that he spent the last 30 years of his life in a determined effort to repudiate it.

Two of the four 1905 papers were indeed on relativity. The first, completed in June, laid out the foundations of his new view of space and time, showing that distances and durations are not absolute, as everyone since Newton had thought, but instead are affected by one's motion. Clocks moving relative to one another tick off time at different rates; yardsticks moving relative to one another measure different lengths. You don't perceive this because the speeds of everyday life are too slow for the effects to be noticeable. If you could move near the speed of light, the effects would be obvious.

The second relativity paper, completed in September, is a three-page addendum to the first, which derived his most famous result, E = mc^2, an equation as short as it is powerful. It told the world that matter can be converted into energy - and a lot of it - since the speed of light squared (c^2) is a huge number. We've witnessed this equation's consequences in the devastating might of nuclear weapons and the tantalizing promise of nuclear energy.

The third paper, completed in May, conclusively established the existence of atoms - an idea discussed in various forms for millenniums - by showing that the numerous microscopic collisions they'd generate would account for the observed, though previously unexplained, jittery motion of impurities suspended in liquids.

With these three papers, our view of space, time and matter was permanently changed.

Yet, it is the remaining 1905 paper, written in March, whose legacy is arguably the most profound. In this work, Einstein went against the grain of conventional wisdom and argued that light, at its most elementary level, is not a wave, as everyone had thought, but actually a stream of tiny packets or bundles of energy that have since come to be known as photons.

This might sound like a largely technical advance, updating one description of light to another. But through subsequent research that amplified and extended Einstein's argument (see Figures 1 through 3), scientists revealed a mathematically precise and thoroughly startling picture of reality called quantum mechanics.

Before the discovery of quantum mechanics, the framework of physics was this: If you tell me how things are now, I can then use the laws of physics to calculate, and hence predict, how things will be later. You tell me the velocity of a baseball as it leaves Derek Jeter's bat, and I can use the laws of physics to calculate where it will land a handful of seconds later.

What is less widely appreciated, however, is that physicists call 1905 Einstein's "miracle year" not because of the discovery of relativity alone, but because in that year Einstein achieved the unimaginable, writing four papers that each resulted in deep and formative changes to our understanding of the universe. One of these papers - not on relativity - garnered him the 1921 Nobel Prize in physics. It also began a transformation in physics that Einstein found so disquieting that he spent the last 30 years of his life in a determined effort to repudiate it.

Two of the four 1905 papers were indeed on relativity. The first, completed in June, laid out the foundations of his new view of space and time, showing that distances and durations are not absolute, as everyone since Newton had thought, but instead are affected by one's motion. Clocks moving relative to one another tick off time at different rates; yardsticks moving relative to one another measure different lengths. You don't perceive this because the speeds of everyday life are too slow for the effects to be noticeable. If you could move near the speed of light, the effects would be obvious.

The second relativity paper, completed in September, is a three-page addendum to the first, which derived his most famous result, E = mc^2, an equation as short as it is powerful. It told the world that matter can be converted into energy - and a lot of it - since the speed of light squared (c^2) is a huge number. We've witnessed this equation's consequences in the devastating might of nuclear weapons and the tantalizing promise of nuclear energy.

The third paper, completed in May, conclusively established the existence of atoms - an idea discussed in various forms for millenniums - by showing that the numerous microscopic collisions they'd generate would account for the observed, though previously unexplained, jittery motion of impurities suspended in liquids.

With these three papers, our view of space, time and matter was permanently changed.

Yet, it is the remaining 1905 paper, written in March, whose legacy is arguably the most profound. In this work, Einstein went against the grain of conventional wisdom and argued that light, at its most elementary level, is not a wave, as everyone had thought, but actually a stream of tiny packets or bundles of energy that have since come to be known as photons.

This might sound like a largely technical advance, updating one description of light to another. But through subsequent research that amplified and extended Einstein's argument (see Figures 1 through 3), scientists revealed a mathematically precise and thoroughly startling picture of reality called quantum mechanics.

Before the discovery of quantum mechanics, the framework of physics was this: If you tell me how things are now, I can then use the laws of physics to calculate, and hence predict, how things will be later. You tell me the velocity of a baseball as it leaves Derek Jeter's bat, and I can use the laws of physics to calculate where it will land a handful of seconds later.

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