When this theory was first published, it was said thai it could be understood by only a dozen or so scientists in thw whole world! So obviously, I cannot even begin to try to explain it in any technical data here. But it should be useful to have a general idea of whatEinstein was dealing with, the problem he was concerned with.
Everybody knows from experience that all motion is "relative." This means that it can only be measured in relation to something else. For example, you're sitting in a railroad train and you look out of the window. As you see things moving by quickly, you know you're in motion. But there's a man sitting opposite you, and relative to him you're not moving at all!
So the existence of motion can have meaning only when it is considered relative to something which is fixed. That's the first basic part of Einstein's theory. We may state it as: The motion of a body travelling at uniform speed through space caannot be detected by obeservation made on the body alone.
The second basic part of Einstein's theory said that only absolute unchanging quantity in the universe was the speed of light. Now, we know this to be about 186,000 miles per second. But it is really a fantastic idea to be able to imagine that this cannot change. Here is why this is so strange: If a car is going at 60miles an hour, we mean that its speed, measured by a someone standing still, is 60 miles per hour. If it passes a car travelling in the same direction at 40 miles per hour, it passes it at a speed of 20 miles per hour. If the second car, instead of travelling in the same...