Note to reader: I am not a physicist. The last physics class I took was in high school. This explanation of a certain Swiss patent clerk's brilliant theory is based on what I have learned from my own reading on the subject. Caveat lector. I must mention George Boolos' published paper, wherein he explains the incompleteness theorems in monosyllables. That was my inspiration for this post, really an exercise in constrained writing. If you find a word of more than one syllable below, and tell me, I will send you one US dollar. Pointing out any other type of error will also be appreciated, but not remunerated.
First: is light made up of bits or is it a wave? Some said "bits." Some said "wave." Then, it was shown that light does seem to be a wave. But a wave of what? Take sound. Sound can be a wave of air. What is light a wave of? This means: through what stuff does light move? There is no air in space. Thus, there is no sound in space. (There, no one can hear you scream.) But in all of space, through each place we can think of, light moves. From far stars to Earth, through what seems to be no stuff, light comes. Thus, if the waves of light move through a thing, we should find this stuff in all of space. It would have to be a strange kind of thing. But, a good thing. For if there was such stuff, we could tell once and for all if you move, or if I move, "for real." To move for real would be to move in the "eyes" of this great, "in all places" stuff. You might see me move past you, but if you see that I move--just so--with this great stuff, it is you who moves "as the world sees it," and I, in fact, stand still. It is the same as the man in the train who looks at a field and sees the field move, while he feels that he is at rest. We all think the field is at rest, and it is he who moves. But, in fact, with some more thought we note that the field, and the whole Earth, moves, from the view of the sun. Who is right "for real"? The man in the train, the man in the field, or the man on the sun, or none of them? Our great stuff will tell us. That which brings light and stands still so we may judge what else stands still: this is what our great stuff must be.
Earth would move through this great stuff. We should find that light that moves with the Earth does not move at the same speed as light that does not go that way. This is like when you are in a train, and see a train pass by which goes towards the rear of your train. It seems to go quite fast, the way you see things. But a train that moves with your train, next to you, might seem to stand still, the way you see things. In one case you move with a train, in one case the train moves towards your rear. Now back to light. We did not find what we thought we would find. In fact, we found this is not the case. Light moves at the same speed in each case. Light does not seem to care how fast you move when you check its speed. It will be the same each time.
Why? This is just a fact. Wow! This is our first claim of faith. Our next and last claim of faith: if you move in the same way as time goes on (that is, you do not gain or lose speed, and you just move on the same line), then the laws of the world are the same for you as they are for me if I move like that too. This means, the world does not care how fast I go or how fast you go, just that my speed stays the same, your speed stays the same, and we each stay on our lines (but you and I do not need to share the same speed). Then, the world will act for you as it does for me. (The way we must write the "rules of the world" in each case will be the same.) The claim used to be that some laws of the world are like this. Now, we say that all laws of the world are like this. Wow! These two claims are a whole new way to look at the world, as we shall see.
Some weird things come from these claims. First, as I see your speed go up and up, I see you start to shrink! And as your speed goes up and up, I will see less time pass for you than for me. And you will think I shrink and that less time has passed for me! That is, to know how big I would judge you to be and how much time I would judge to pass for you, I need to know how fast you move as I see it. These things are not the same for all speeds. Time and space are not fixed for all the world. You have your rods to check lengths and your clocks to check the time, and I have mine.
Next, what does it mean for two things to come to pass at the same time? If they come to pass at the same place, this is clear. What if they do not come to pass at the same place? What if thing One is far from thing Two? Then you might say they come to pass at the same time, and I might say they do not, and we are each right. "Same time" for you need not mean the same thing as "same time" for me. There is no "same time" for all the world. If thing One is quite far from thing Two for me, it can be that it is wrong to say "One came to pass first," wrong to say, "Two came to pass first," and wrong to say "One and Two came to pass at the same time"! It is like this: if you ask One, One will say "For me, Two is not far from me or close to me in time. Two is just quite far from me in space. And that is all you can say, if you do not bring up the way you see things." And the same goes for Two. For me, it could look like One and Two come to pass at the same time, while for you, it looks like they do not.
Let us now go back to the great stuff that light would move through as waves. In fact, we had just one way to "see" this stuff. This was to see light move at speed one this way, but speed two that way, and so on. But, we found that light moves at the same speed each way. So, there is no way to see this odd stuff, no way to prove that it is there. And there seems to be no need for a thing that is at rest "for real." What would this mean? As claim two says, the laws of the world are the same for those who move in the way we said, if their speeds are the same or not, or on the same line or not. There is "at rest" for you, and "at rest" for me, but no "at rest" for the world. The field moves "for real" just as much as the train moves "for real": in some pair of eyes. Thus, our great stuff fades to nil. The world cares naught for it, and we say: it is not! So, light is like a wave but not like a wave. It needs no "air" to move through. The void of space does not hear, but it does see!
Most strange of all: speeds do not add as we might think they add. Let us see it this way. You are in a field next to train tracks. As you judge it, I am on a train that moves at speed One. I run through a train car at speed Two (as the train would "judge" it, or as a chap in a seat on the car would judge it). How fast do you, in the field, judge me to move? We want to say: One plus Two. This is wrong! It takes more math, but math or no math we can see why it is strange. If you are on a train that moves at a speed, One, close to the speed of light (as I judge it), and stand still, and have great strength, and throw a ball at some great speed Two (as the train would "judge" it; let this speed be great but still much less than the speed of light and the speed of this train), I will see the ball move at a speed less than One plus Two! In fact, it will be quite close to One, the speed of the train. When we put a speed on top of a speed, and want to know the third, "sum" speed, to just add them up is wrong. If you do not think this is strange, think on it more!
This is so weird; how can it be right? The world does not seem to act this way. Well, if we want to see the world act this way (to catch it in the act), we need stuff to move at quite a fast speed (as we judge it). Stuff that moves that fast is hard to come by. So, we do not see these weird things. But, these weird things are real. We see them when we do find stuff, like small, small stuff, that can move at high speeds. In fact, we have found stuff that moves so fast that time for it is quite slow (as we see it), and how far it has to go to get to us is quite small (as it sees it), and this lets that stuff make it to us from space! If time did not move so slow for it, it would "melt" too soon in the top parts of Earth's air for us to see it on the ground! As it turns out, our two claims of faith seem true.
Now, where are we? We made two claims of faith to grasp why we see light move as it does, looked at some strange claims that come from them, and now at the end we have mixed up space, time, and the way things move. Well, do not be mad: the world has mixed them up! Is this all? No. We have not brought in force at all. We have just part of the truth, for the nice but weird case where no force acts. How does a pull or a push change things? We will leave that for a day to come.