"... historically the fourth dimension has been considered a mere curiosity by physicists. No evidence has ever been found for higher dimensions. This began to change in 1919 when physicists Theodor Kaluza wrote a highly controversial paper that hinted at the presence of higher dimensions. He started with Einsteins theory of general relativity, but placed it in five dimensions (one dimension of time & four dimensions of space; since time is the fourth space-time dimension, physicists now refer to the fourth spatial dimension as the fifth dimension). If the fifth dimension were made smaller and smaller, the equations magically split into two pieces. One piece describes Einsteins standard theory of relativity, but the other becomes Maxwells theory of light.

This was a stunning revelation, perhaps the secret of light lives in the fifth dimension! Einstein himself was shocked by the solution, which seemed to provide an elegant unification of light and gravity. (Einstein was so shaken by Kaluza's proposal that he mulled it over for two years before finally agreeing to have this paper published.) Eisntein wrote to Kaluza, "The idea of achieving [ a unified theory] by means of a five dimensional cylinder would never have dawned on me... at first glance, I like your idea enormously... the formal unity of your theory is startling."

For years physicists had asked the question: if light is a wave, then what is having? Light can pass through billions of light-years of empty space, but empty space is a vacuum, devoid of any material. So what is waving in the vacuum? With Kaluza's theory we had a concrete proposal to answer this problem: light is ripples in the fifth dimension. Maxwell's equations, which accurately describe all the properties of light, emerge simply as the equations for waves traveling in the fifth dimension."

This was a stunning revelation, perhaps the secret of light lives in the fifth dimension! Einstein himself was shocked by the solution, which seemed to provide an elegant unification of light and gravity. (Einstein was so shaken by Kaluza's proposal that he mulled it over for two years before finally agreeing to have this paper published.) Eisntein wrote to Kaluza, "The idea of achieving [ a unified theory] by means of a five dimensional cylinder would never have dawned on me... at first glance, I like your idea enormously... the formal unity of your theory is startling."

For years physicists had asked the question: if light is a wave, then what is having? Light can pass through billions of light-years of empty space, but empty space is a vacuum, devoid of any material. So what is waving in the vacuum? With Kaluza's theory we had a concrete proposal to answer this problem: light is ripples in the fifth dimension. Maxwell's equations, which accurately describe all the properties of light, emerge simply as the equations for waves traveling in the fifth dimension."