any moving object can change its speed only if it acts a force.Then he will be accelerated.The higher the value, the faster the rate of change.Nevertheless, from the point of view of classical mechanics, standing acceleration can increase the speed of the body to arbitrarily large values.Thus, it would seem, the spacecraft can reach the speed of light, or even surpass it.The main thing that he had enough fuel, space and time to disperse.
theory of relativity, Albert Einstein created, amends this theory.According to its formula, the closer the speed of the body to the speed of light, the harder it is to increase it even more.The mass of a fast moving body begins to increase, and when accel
erating to the speed of light would become infinite.Therefore, no object with mass can not move at the speed of light.
photons (the smallest particles of light) have no mass.However, they suffer not only energy, but also the pulse, and hence can transmit the motion.Based on this fact, scientists of the twentieth century, proposed the idea of ​​a photon engine.A powerful stream of light coming from the spacecraft, will, according to the law of jet propulsion, push it forward.And since the rate of flow is equal to the speed of light, the photon spaceship can fly almost as fast.However

jet thrust force created by light, very small.If you only use it starship crackdown would continue for centuries.Therefore, it was suggested that the ship left on a certain initial velocity using more conventional jet engines and photon beam is turned on only for cruise traffic.
Although surpass the speed of light is not possible, a way to overtake the light still exists.The fact that light travels at maximum speed only in a pure vacuum.In any other environment, it slows down and sometimes very strongly.

By passing light through specially prepared material, the researchers reduced its speed up to tens of kilometers per hour.Finally, using a pair of rubidium cooled to almost absolute zero, the light managed to bring almost to a complete halt.The photons which have entered into this stuff, come to light only after many years.