The special theory of relativity is taken to be a non-intuitive theory. This means that the concepts are so far removed from everyday experience that it goes against all common sense. This is true if your not a scientist. Scientist spend all day thinking in this manner, so to them it is common sense. Please let me explain.
The idea that mass is directly proportional to energy, is probably one of the biggest non-intuitive results that the theory predicts. Another idea of this theory is that time ticks differently depending on how fast you are moving relative to another observer. The so called twin-paradox is all about this idea. Imagine that I was your long lost twin brother, and back in the year 2005 I got into a spaceship and cruised at near the speed of light – 186,000 miles per second, while you stayed here on Earth and waited for my return. If you didn’t have any idea of Einsteins special theory of relativity, you might of had no problem staying behind. However, as it would turn out, you do know something about this theory, and you wish to stay with me so that we don’t age differently. Because you knew that if I had gone for a cruise at near the speed of light, you would have aged by roughly 7 times longer than I would. How can this be you ask?
Well to be quite honest, it’s rather very simple. You see the speed of light is the key here. Nothing can ever go faster than the speed of light, so when you approach that ultimate speedlimit, some very strange effects take place. For instance, the energy that goes into the acceleration can not just disappear – it must go somewhere, and this somewhere is the mass of the ship. So this means that as the ship approaches the the speed of light, its mass increases without limit. This is what someone would measure if they weren’t physically on that ship. To the observer who is still on the ship everything appears normal. You see these effects must happen in order to ensure that every observer measures the speed of light to be the same.
Another effect here is known as Lorentz contraction. This is also due to the amazing speed of light. To someone whatching a very fast spaceship (if they could), they would notice that the ship is shrinking in the direction of motion as the ship approaches the speed of light. Once again this effect must happen to ensure that every observer measures the speed of light to be the same.
To sum up the theory of special relativity in a nutshell…Space and time are connected into a 4 deminsional continuum. My space and time is a mixture of your space and time, and vis-versa. Mass is directly proportional to energy. The lengths and times that one observer measures are relative to velocity of light. Meaning that as your velocity becomes closer and closer to that of lights, these effects become more and more pronouced.