You are standing there, as square cube from 1 by 1, by 1 in the center of a 3 dimensional plane. All over the plane there cubes floating in the air of the size of 1 by 1, by 1. But 1, by 1, by what? Centimeters? Millimeters? Meters? Kilometers? You don’t know. So you take a ruler and measure yourself. It turns out your a centimeter high! You stand there as a cube, watching at the other cubes. Nothing changes when you are looking around. However, you forgot how tall you were. So you take your ruler again, and as a complete shock, you measure yourself at 6 by 6, by 6 centimeter. That was totally different then before. You look around, but nothing is changing is size. How weird! You measure yourself again, and suddenly you are 13 centimeters tall, what the hell is going on?
It seems like everything around you is expanding, including yourself! Things change relative to yourself, but when you are changing yourself at the same rate, in a coherent way, you won’t see the change. You look around and suddenly the other cubes change in size, they seem to get larger while you seem to stay at the same size. Or you might even seem to get smaller, you don’t know. So you take your ruler again, and you see that you are still increasing in size, even more weird! It seems then, that the other cubes just increased size with a higher speed than you. The acceleration of the cubes was not coherent with each other. Or there might be a third event, and that will be that ruler by itself is inconsistent. It might give the opposite measurement of what really happened. Imagine that the ruler says that you doubled in size from 1 cm to 2 cm, relative to the other cube which stayed the same size (1 cm). How could you figure out that it is not the other way around? It could be that the other cube shrunk from 1 to 0,5 cm, and you stayed the same size (1 cm). Without something that oversees the two parties changing from size, you can’t establish this. Something that can measure the size of both cubes at the same time can see what is happening, and what is changing.
A third cube might see the other two cubes change in size relative to each other and could say which one is expanding and which one is shrinking. However, this third cube still doesn’t know about the exact sizes of the cubes. They all might be expanding in size all the time, thus only the relative difference between the two cubes and the third cube could be established. With the phrase, “everything is relative”, it is said correctly; we have no absolute measure of space because we wil never know how fast everything might expand, when everything is expanding. We might even see things shrink even though they are expanding. The question will always remain; relative to what are you changing your size, speed, or even shape. Why shape? That is something for a different story.