Sunday, June 16, 2013

Two people travelling on a curved surface of a sphere

THE GOLDEN RATIO: The Story of Phi, The World's Most Astonishing Number, by Mario Livio, (Broadway Books, New York: 2002), p.30-31


“Today, while we may be amused by some of the Pythagorean fanciful ideas, we have to recognize that the fundamental thought behind them is not very different from that expressed by Albert Einstein (in Letters to Solovine): “Mathematics is only a means for expressing the laws that govern phenomena.” Indeed, the laws of physics, sometimes referred to as the “laws of nature,” simply represent mathematical formulations of the behavior that we observe all natural phenomena to obey. For example, the central idea in Einstein's theory of general relativity is that gravity is not some mysterious, attractive force that acts across space but rather a manifestation of the geometry of the inextricably linked space and time. Let me explain, using a simple example, how a geometrical property of space could be perceived as an attractive force, such as gravity. Imagine two people who start to travel precisely northward from two different points on Earth's equator. This means that at their starting points, these people travel along parallel lines (two longitudes), which, according to plane geometry we learn in school, should never meet. Clearly, however, these two people will meet at the North Pole. If these two people did not know they were really travelling on the curved surface of a sphere, they would conclude that they must have experienced some attractive force, since they arrived at the same point in spite of starting their motions along parallel lines. Therefore, the geometrical curvature of space can manifest itself as an attractive force. The Pythagoreans were probably the first to recognize the abstract concept that the basic forces in the universe may be expressed through the language of mathematics.”