Albert Einstein is perhaps the most famous scientist of the 20th century. One of his most well-known accomplishments is the formula E=mc^2. It means that energy is equal to the mass multiplied by the square of the speed of light.
Einstein realizes that mass and energy are really different forms of the same thing. Mass can be turned into energy and energy into mass. For example, here is one kilogram of pure water. If it could be suddenly turned into energy, it would become:
=90,000,000,000,000,000 Joules(焦耳) (ninety thousand trillion Joules)
This is the equivalent of the energy that we burn 10 million gallons of gasoline. That’s really unbelievable. Here in the formula, “c” represents the speed of light because light speed is a constant. It is always 300,000,000 meters per second invacuum under any circumstances.
Now let me try to explain it.
Suppose we are now riding a car and trying to chase a train. The speed of the train is 100 miles per hour and the speed of our car is 99 miles per hour. Then we can see the train is running away from us by the speed of 1 mile per hour. Now let’s replace the train with a beam of light, or suppose that the train’s speed has the same property with light. Then what we see is that the light beam is not running away from us by the speed of 1 mile per hour. It is still running away from us by the speed of 100 miles per hour. In that case, we don’t believe our eyes and try to accelerate our car to the speed of 99.99999 miles per hour. We consider that we are going to catch up with the beam of light, but when we look out of the window, the light beam is still flying away from us by the speed of 100 miles per hour. It seems like we are not moving.
It is very weird. How can it happen this way?
Einstein himself is very shocked when he finds out this phenomenon. He studies it more, and finally comes to an amazing conclusion. For the people riding in the car, TIME BECOMES SLOWER. If there is a bystander on the road and he uses a telescope to watch us, he can see that everyone in the car moves very slowly and he can see the car is squeezed into a flat thing like an accordion.
Scientists have proved this theory. Whatever our speed is, the light speed is always a constant-- that is, 300,000,000 meters per second. This is because when we move faster, the clock runs slower and the tool we use to measure the distance becomes shorter. Therefore, the result of the measurement is always the same.
Can we see or feel this effect? No. Because when we move near the speed of light, our minds would think with a slower process, and our bodies become thin in size. So we cannot perceive the change. Nature plays tricks on us. This is called “Special Relativity.”(狹義相對論). With further studies, Einstein finally figures out the distinguished formula E=mc^2. This formula has completely changed our world.