http://www.ck12.orgCHAPTER
(^25) Relativity
Chapter Outline
25.1 The Theory of Special Relativity
25.2 THETHEORY OFGENERALRELATIVITY
25.3 REFERENCES
According to the special theory of relativity, time on an object traveling near the speed of light passes more slowly
than time on a non-moving reference object. This phenomenon is called time dilation. There is an interesting
consequence of time dilation. Imagine two twins, one who stays on earth (non-moving reference object) while the
other twin travels into space on a space ship traveling at 90% of the speed of light. After reaching some distant point,
the traveling twin immediately turns around and returns to earth. If the trip covered 4.3 light years (distance), the
stay-at-home twin sees the trip take 9.6 years on his normal clock. The traveling twin finds that the trip according
to his watch (having undergone acceleration and high speed velocity) takes only 4.0 years. The closer the traveler
gets to the speed of light, the slower time moves and the less the traveler ages.
Therefore, when the traveling twin returns home, he will find that his twin brother has aged 5.6 years more than he
has.
In this unit, you will come face to face with Einstein’s special theory of relativity and some of the very strange
conclusions resulting from it.