A lot of people think about the theory of relativity as, well, nothing. Some people know that Albert Einstein was the one who thought about and created this theory as in E=MC^2. But what the theory is about is going the speed of light. As humans, we can only go so fast with the technology today, jets and stuff but, we might NEVER not ever be able to travel the speed of light. In retrospect, the speed of light is fast, insanely fast. If a train was to go the speed of light round and round the Earth, it would pass one place 8 times every second. That is incredible.
Now in the time of Einstein a hundred years ago, he didn't have all this technology and calculating ability with the computers these days. So he did a thought experiment. He thought about what would happen if we did travel the speed of light. Imagine your in that speed of light train and you hold a mirror up. Would you be able to see your reflection? If your going at the speed of light, then the light bouncing of off you would NEVER reach the mirror and bounce off. A simple solution Einstein thought was that light would just travel at TWICE it's speed. So you would be able to see your reflection.
Now the question is if light was twice as fast inside the train, wouldn't it be twice as fast to someone outside the train? It was twice as fast! What Einstein said was that the only way that this would work is if time inside the train was slower than the time outside the train. This is what started theories on time travel when you go the speed of light. The only problem was that if you do go the speed of light. Time will just stop... Like a freeze frame. Think about it
