Parallel Worlds Read Online Free PDF Page B

radically new picture of the universe in which the mysterious laws
governing celestial bodies were identical to the laws governing Earth. The
stage of life was no longer surrounded by terrifying celestial omens; the same
laws that applied to the actors also applied to the set.
    BENTLEY'S PARADOX
    Because Principia was such an ambitious work, it raised the first disturbing
paradoxes about the construction of the universe. If the world is a stage, then
how big is it? Is it infinite or finite? This is an age-old question; even the
Roman philosopher Lucretius was fascinated by it. "The Universe is not
bounded in any direction," he wrote. "If it were, it would
necessarily have a limit somewhere. But clearly a thing cannot have a limit
unless there is something outside to limit it . . . In all dimensions alike, on
this side or that, upward or downward throughout the universe, there is no
end."
    But Newton's
theory also revealed the paradoxes inherent in any theory of a finite or
infinite universe. The simplest questions lead to a morass of contradictions.
Even as Newton was basking in the fame brought to him by the publication of Principia, he discovered that his theory of gravity was necessarily
riddled with paradoxes. In i692, a clergyman, Rev. Richard Bentley, wrote a
disarmingly simple but distressing letter to Newton. Since gravity was always
attractive and never repulsive, wrote Bentley, this meant that any collection
of stars would naturally collapse into themselves. If the universe was finite,
then the night sky, instead of being eternal and static, should be a scene of
incredible carnage, as stars plowed into each other and coalesced into a fiery
superstar. But Bentley also pointed out that if the universe were infinite,
then the force on any object, tugging it to the left or right, would also be
infinite, and therefore the stars should be ripped to shreds in fiery
cataclysms.
    At first, it
seemed as if Bentley had Newton checkmated. Either the universe was finite (and
it collapsed into a fireball), or it was infinite (in which case all the stars
would be blown apart). Either possibility was a disaster for the young theory
being proposed by
    Newton. This
problem, for the first time in history, revealed the subtle but inherent
paradoxes that riddle any theory of gravity when applied to the entire
universe.
    After careful
thought, Newton wrote back that he found a loophole in the argument. He
preferred an infinite universe, but one that was totally uniform. Thus, if a
star is tugged to the right by an infinite number of stars, this is canceled
exactly by an equal tug of another infinite sequence of stars in the other
direction. All forces are balanced in each direction, creating a static
universe. Thus, if gravity is always attractive, the only solution to Bentley's
paradox is to have a uniform, infinite universe.
    Newton had
indeed found a loophole in Bentley's argument. But Newton was clever enough to
realize the weakness of his own response. He admitted in a letter that his
solution, although technically correct, was inherently unstable. Newton's
uniform but infinite universe was like a house of cards: seemingly stable, but
liable to collapse at the slightest disturbance. One could calculate that if
even a single star is jiggled by a tiny amount, it would set off a chain
reaction, and star clusters would immediately begin to collapse. Newton's
feeble response was to appeal to "a divine power" that prevented his
house of cards from collapsing. "A continual miracle is needed to prevent
the Sun and the fixt stars from rushing together through gravity," he
wrote.
    To Newton, the
universe was like a gigantic clock wound up at the beginning of time by God
which has been ticking away ever since, according to his three laws of motion,
without Divine interference. But at times, even God himself had to intervene
and tweak the universe a bit, to keep it from collapsing. (In other words,
occasionally God has to intervene to prevent