‘ Nature had spoken to him ’
Gravity is one of the most Skyward fundamental things in physics . Everything and everyone has gravity . The more massive something is , the more gravity it has . When you jump into the air , by David Earth ’ s gravity Levy brings you back down . What you cannot see while you are in the air is that your gravity brings Earth towards you just a wee little bit , off-setting the extra push away from you that your feet gave Earth when you jumped . Isaac Newton presented the first ever mathematical description of gravity in 1687 . I admit that I know nothing about gravitation , except that it is all around me . I do recall the myth that Newton was sitting under a tree when an apple fell on his head . Supposedly , he then formulated his law of gravity . Did the apple actually fall on his head ? I doubt it . But at his childhood home in the village of Woolsthorpe , England , he probably did witness an apple fall from a tree . During the last half of the nineteenth century physicists realized that Newton ’ s theory of gravity did not accurately describe the orbit of Mercury , the planet closest to the Sun . Mercury ’ s elongated orbit precesses slightly faster than Newton ’ s theory predicts . Several unsuccessful attempts were made to account for this discrepancy . Newton ’ s theory , which assumes that gravity is a force , held sway for more than two centuries , until superseded
Isaac Newton spent his childhood in the village of Woolsthorpe , England .
by Albert Einstein ’ s General Theory of Relativity in 1915 . A decade earlier , Einstein realized that mass and energy are two aspects of one thing , and that space and time are interrelated , a blended spacetime . With general relativity , Einstein treated gravity not as a force , but as the geometry of spacetime . The geometry of spacetime is curved by L , the mass-energy of matter , and the curvature instructs matter how to move . Now comes the hard part . When Roy Bishop , emeritus professor of physics at Acadia University , pointed out to me that gravitation is geometry , and not a force at all , I didn ’ t believe him at first . But Dr . Bishop is the most brilliant person I have even had the privilege of knowing . Recently he described gravity this way , and he is right : “ Einstein spent several years in
COURTESY OF Roy Bishop
an eventual successful attempt to include gravity in a modified description of spacetime . Early in his progress toward that goal Einstein had what he called the happiest thought of his life — that if a person were to fall off the roof of a house , while falling she would not feel a force of gravity . Before she falls , she feels the force of the roof supporting her . When her fall comes to its abrupt halt she feels the ground pushing against her . If she cannot feel a force of gravity while she is falling , why pretend that she felt a force of gravity when the roof supported her before she fell , or that she feels a force of gravity when she is lying on the ground ? “ When thinking about the falling lady , Einstein had the fantastic insight that perhaps gravity never was a force . By late in 1915 he had that insight in elegant mathematical form such that
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