Albert Einstein receives a letter that leaves him speechless. It comes from a German mathematician unknown to him: Theodr Kaluza. He combines gravity and electromagnetic equations by introducing a fifth dimension (in addition to the four space-time dimensions). This is the marbling of physics, as Einstein intended it. He saw space-time as “marble”: clean, beautiful, elegant, while matter is “wood,” a hideous, confusing collection of random shapes (referring to the plethora of particles and subparticles that form crystals, rocks, etc.). Kaluza, introducing a fifth dimension (fourth spatial dimension), describes light as a disturbance in this fifth dimension. Kaluza has found the first clue to transforming wood into marble. But where is this fifth dimension? Kaluza has a ready answer: it’s coiled so tightly that not even an atom can fit inside. Klein will demonstrate in 1926 that it must be of the size of 10-35m or the Planck length.
