Einstein's Relative Time
In the end of the 19th and beginning of the 20th centuries there was a change developing in the way that time was viewed in physics. The development of the equations of electro-magnetics by James Maxwell lead others to investigate their consequences. Among those was non other than Albert Einstein. Albert Einstein developed first a special theory of relativity, in 1905, that showed how light waves behaved in different reference frames. Later he developed a general theory of relativity that explains gravity and the geometry of the universe. In both of these theories time is no longer immutable. Indeed, different observers in relative frames measure different times. As the theories gained more experimental verification the old ideas about the nature of time crumbled away. Only days before his death Einstein was quoted as saying ``The distinction between past, present, and future is only a stubbornly persistent illusion.''