Imagine you are a three-dimensional cube in a mathematical plane. You look around you, and there is another cube floating in the air of the same size. But how large are you? A few centimetres? Millimetres? Meters? Kilometres? You don’t know. You take a ruler and measure yourself. It turns out you’re a centimetre high! You stand there as a cube, watching at the other cube. 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 being 6 by 6, by 6 centimetre. That was totally different than before. You look around, but nothing is changing in size. How weird! You measure yourself again, and suddenly you are 13 centimetres tall, what the hell is going on?
It seems like the other cube is expanding, and you expand with it! The other cube changes in the size relative to yourself, but when you are changing at the same rate, in a coherent way, you won’t see the change. You look around and suddenly the other cube changes in size, they cube seems 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 cube just increased in size with a higher speed than you. The acceleration of the other cube was not coherent with your acceleration. Suddenly, the other cube starts to shrink. But does it shrink or does it grow less fast relative to your growth? You have no clue. Without something that oversees the two parties changing from size, you can’t establish this. You need something that can measure the size of the both cubes at the same time, to 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 will 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.
When everyone around you becomes older, you wouldn’t feel older in your group of peers. When humanity becomes more reliant on technology, you wouldn’t notice is that much because everyone becomes reliant. You’re just a cube looking around.