If there was some universal frame of reference, some master clock and absolute ruler, as Newton suggested, then the speed of light should only be the speed that it is relative to that absolute frame, because that absolute frame is the benchmark against which to measure all motion. The entities of our universe must know where they are relative to this fixed frame so that gravity can be the correct strength at the proper times and the proper places. This is all a mathematical framework that provides the mechanisms for computing gravitational forces, but the need for that framework is paramount in Newton's work.)Īnd so in Newton's view of gravity, every gravitational interaction must be computed in regard to that universal, fixed, absolute frame of reference. There is no giant clock floating out there in the void of space, ticking by with absolute time, nor are there literally grids of marked rulers crisscrossing the cosmos. (This is not meant to be taken literally, I should mention. ![]() And so Newton conceived of the cosmos as a vast fixed grid, a series of universal rules and master clocks, and absolute reference frame from which all other measures could be taken. When I pluck an apple from the tree and let it fall, the apple needs to know how far away from the Earth it is so that it can have the proper rate of acceleration.Įverything in the universe needs to know where everything else is so that gravity can act with the appropriate amount of force. When the sun reaches out with its gravitas and instructs all the planets, even mighty Jupiter, where to move next, those planets need to know where they are relative to the sun. Once Newton hit upon his idea for a conception of gravity, a force emanating from and connecting to all objects, he needed a universe to make his force universal. But to understand how Einstein rewrote Newton's insights we first have to rewind the clock back a bit and understand Newton's insights. Einstein discovered that what we once thought immutable was nothing but. ![]() ![]() And that singular feature is right there in the name: relative.
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