In the mid-1920s, Einstein was still not satisfied. He would try one last time to produce another world-class theory. But on his third try, he failed. He was searching for the “Theory of Everything” -- a theory that would explain all the familiar forces found in nature including light and gravity. He coined this theory the Unified Field Theory. He died with unfinished ideas of various manuscripts on his desk.
Ironically, the source of Einstein’s frustration was the structure of his own equation. For 30 years, he was disturbed by a fundamental flaw in this formulation. On one side of the equation was the curvature of space-time, which he likened to “marble” because of its beautiful geometric structure. However, he hated the other side of this equation describing matter-energy which he considered to be ugly and he compared to “wood”. While the “marble” of space-time was clean and elegant, the “wood” of matter-energy was a horrible jumble of confused, seemingly random forces from subatomic particles, atoms, polymers, and crystals to rocks, trees, planets, and stars.
Einstein’s grand strategy was to "turn wood into marble" – that is, to give a completely geometric origin to matter. In retrospect, we can probably spot Einstein’s error. We recall that the laws of Nature simplify and unify in higher dimensions. Einstein correctly applied this principle twice : in Special and in General Relativity. However on his third try, he abandoned this fundamental principle. He blindly tried a number of purely mathematical approaches. He apparently thought that “matter” could be viewed as kinks, vibrations, or distortions of space-time. However, without any more solid leads or experimental data, this idea led to a blind alley. It would be left to an obscure mathematician to take the next step which would us to the 5th-dimension.
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