Why is it not easy to describe the Universe?

When you hear the word 'Universe', what do you think of? You think of a large and unimaginable expanse of dust, gas, stars, clouds, galaxies, and life. It is difficult to describe it exactly, because no one knows what it actually consists of. There may be many distant worlds in the Universe about which we know nothing. Even every empty space is part of the Universe, and so are matter, time, and energy. Some scientists say that if you could look at the entire universe at once, it would look like a giant spider web, made up of billions of galaxies, and trillions and trillions of stars. If you find this a bit too much to grasp, don't worry! Even the greatest scientists have not yet solved the mystery of Universe!