why their is a time dilation and length contraction if a body tend to move with the speed of light ???
Answers
In a nutshell, the Special Theory of Relativity tells us that a moving object measures shorter in its direction of motion as its velocity increases until, at the speed of light, it disappears. It also tells us that moving clocks run more slowly as their velocity increases until, at the speed of light, they stop running altogether. In fact, it also tells us (as we will see in subsequent sections) that the mass of a moving object measures more as its velocity increases until, at the speed of light, it becomes infinite.
Thus, one person’s interval of space is not the same as another person’s, and time runs at different rates for different observers traveling at different speeds. To some extent, the faster you go, the slower you age and the slimmer you are! The reason this is not obvious in everyday situations is that the differences at everyday speeds are infinitesimally small, and only really become apparent at speeds approaching that of light itself (“relativistic” speeds). The closer the speed of an objects approaches to the speed of light, the more warped lengths and time intervals become.
The amount of length contraction and time dilation is given by the Lorentz factor, named after the Dutch physicist Hendrik Lorentz, who had been exploring such transformation equations since as early as 1895, long before Einstein began his work (indeed some would claim that Lorentz and Henri Poincaré between them anticipated almost everything in Einstein's Special Theory of Relativity). The Lorentz factor, γ (gamma) is given by the equation γ ≡ Lorentz Factor, so that the effect increases exponentially as the object's velocity v approaches the speed of light c. Thus, the calculations show that at 25% of the speed of light, the effect is just 1.03 (a mere 3% slowing of time or contraction of length); at 50% of the speed of light, it is just 1.15; at 99% of the speed of light, time is slowed by a factor of about 7; and at 99.999, the factor is 224. So, if it were possible to travel in a spaceship at, say, 99.5% of the speed of light, a hypothetical observer looking in would see the clock moving about 10 times slower than normal and the astronaut inside moving in slow-motion, as though through treacle