The Universe that we know is composed of atoms, the basic components of the matter we know. The most two commons in the universe are Hydrogen and Helium, but they are many other that you may know like carbon, oxygen etc..
They are grouped together to form stars, planets, gas cloud… and we can see them because they reflect or emit light.
However it turn out that most of the universe is composed of something that we don’t know, and cannot see, as it does not emit anything we can detect, and does not reflect or emit light. In 1933, astronomers found out that certain stars, galaxies or other object seems to turn faster than expected around certain area of space, as if part of space apparently empty was containing something more. Since then this was observed even in apparently empty part of space. Astronomers call this “something”, dark matter. It is not certain still on this day, what dark matter is, we only know it is there in large quantity in the universe because it has a weight that attract visible matter.
The Universe is thought to consist of three types of substance: normal matter, ‘dark matter’ and ‘dark energy’, but scientists are still trying to decide what proportion of each of these matters actually exist. The universe is so big it is very difficult to go into space or look at samples from earth and answer the question in one go. This is because we cannot look at all the world and universe in one life time as a group of scientists, it’s too big to sample. So scientists use physics and chemistry, primarily to try and predict or estimate what is happening in the universe and what it is made of by using statistics or maths.
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