Free E=mc2 by David Bodanis Page B

time she had published original translations of Aristotle and Virgil. Occasionally it would slip, when she did a burst of probability calculations for the gaming table.
    Time passed, and they went back to Cirey. The lime trees were growing ("in this, our delightful retreat," as she wrote), and she had even let Voltaire have his vegetable garden. And then, as she hurriedly wrote in a letter to a friend
    3 April, 1749
    Château de Cirey
    I am pregnant and you can imagine . . . how much I fear for my health, even for my life . . . giving birth at the age of forty.
    It was the one thing she couldn't control. She'd had children shortly after her marriage, but she had been twenty years younger, and even then it had been dangerous. Being this much older, survival was not very likely. Doctors of the time had no awareness that they should wash their hands or instruments. There were no antibiotics to control the inevitable infection; nothing like oxytocin, which can control uterine bleeding. She didn't rage at the clear incompetence of her era's doctors; she just said to Voltaire that it was sad leaving before she was ready. The length of time before her was very clear: the labor was expected in September. She'd always worked long hours; now she sped up, the candles at the desk where she wrote sometimes burning till dawn.
    On September 1, 1749, she wrote to the director of the king's library, stating that he would find in the accompanying package the now complete draft of a major commentary she was doing on Newton. Three days later, the birth began; she survived that, but infection set in, and within a week she died.
    Voltaire was beside himself: "I have lost the half of myself—a soul for which mine was made."
    In time the focus on energy as being proportional to mv 2 began to seem second nature to physicists. Voltaire's polemical skills, passing on the legacy of his lover, helped give it an even stronger boost. In the following century, Faraday and others used mv 2 —this quantity that might transform but never totally disappeared— as they built up their visions of the conservation of all energy. Du Châtelet's analysis and writing had been an indispensable step, though in time her role came to be forgotten; partly because each new generation of scientists tends to be generally neglectful of their past; partly, perhaps, because it was unsettling to hear that a woman could have directed such a large research effort and helped shape the course of subsequent thought.
    The big question, though, is why. Why is squaring the velocity of what you measure such an accurate way to describe what happens in nature?
    One reason is that the very geometry of our world often produces squared numbers. When you move twice as close toward a reading lamp, the light on the page you're reading doesn't simply get twice as strong. Just as with the 'sGravesande experiment, the light's intensity increases four times.
    When you are at the outer distance, the light from the lamp is spread over a larger area. When you go closer, that same amount of light gets concentrated on a much smaller area.
    The interesting thing is that almost anything that steadily accumulates will turn out to grow in terms of simple squared numbers. If you accelerate on a road from 20 mph to 80 mph, your speed has gone up by four times. But it won't take merely four times as long to stop if you apply brakes and they lock. Your accumulated energy will have gone up by the square of four, which is sixteen times. That's how much longer your skid will be.
    Imagine that skid hooked up to some sort of energy collector. A car that's racing along at four times another one's speed, really will generate—really does carry along—sixteen times as much energy. If someone tried to measure energy as simply equal to mv 1 , they'd miss all this. Only by concentrating on mv 2 do these important aspects come out.
    Over time, physicists became used to multiplying an object's mass by the square of its