Science fiction, which nowadays seems to become fact with alarming regularity, delights in stories of time machines which can transport man forwards or backwards in time. There are good scientific reasons to believe that we will never be able to reverse time; but in 1905 and 1915 Albert Einstein, in his theories of relativity, showed that time can behave in a curious way.
It is not really possible to explain or understand Einstein's theories about time, matter and energy without going deeply into physics and mathematics.
But these theories completely altered previous ideas which scientists had about the nature of the universe. Einstein showed that there is no such thing as an absolute measurement of time or space and that speed and position were relative things. He also proved that there is no real difference between matter and energy.
It was through a study of the relationship between time, space and speed that Einstein was led to his theory of relativity, one of the most important landmarks in the history of science.