Atoms are the small particles of which every element is made up of. The atom possesses the properties of its element.
Many astronomers think the Universe started in a Big Bang about 14 billion years back. During those times, the whole Universe was inside a bubble that was 1000s of times smaller compared to a pinhead. It was denser and hotter than anything we can imagine.
Then it suddenly exploded. The Universe that we all know was born. Time, space and matter all started with the Big Bang. In a fraction of a second, the Universe grew from smaller than an individual atom to larger than a galaxy. And it continued growing at a great rate. It is still growing today.
As the Universe expanded and cooled, energy transformed into particles of antimatter and matter. These two opposite kinds of particles largely destroyed one another. But some matter made it. More stable particles known as neutrons and protons began to form when the Universe was one second old.
Over the next three minutes, the temperature decreased below 1 billion degrees Celsius. It was now cool sufficient for the neutrons and protons to come together, building hydrogen and helium nuclei.
Following 300 000 years, the Universe had cooled to about 3000 degrees. Atomic nuclei could finally capture electrons to make atoms. The Universe full of clouds of hydrogen and helium gas.
Normal matter comprises everything we can notice, smell or touch. This matter, which is produced from atoms also comprises stars and planets.
All objects made from atoms pull on one another based on how much matter they contain. This is why a tiny, low mass object including an apple drops towards a lot more massive object, the Earth.
Astronomers think that there must be also another type of invisible 'dark matter' that is spread through the entire Universe. By learning the Milky Way and numerous distant galaxies, they have discovered that visible matter on its own cannot account for their rotation, size and shape. Alone, normal matter would not be able to produce enough gravity to maintain the galaxies together.
Scientists also can tell that there is some unfamiliar material in the space between the stars, due to its gravitational pull influences the path of starlight travelling towards Earth. Dark matter can even behave like a magnifying glass, bending and distorting light from galaxies and clusters behind it. Astronomers can use this effect, referred to as gravitational lensing, to map the distribution of dark matter.
No more than 15% of the matter within the Universe is made from atoms. The rest is dark matter. However, Nobody knows what dark matter consists of. We do know that it does not soak up, emit or reflect light, because not one of our scientific instruments can directly detect it.Numerous scientists think that most dark matter is some unfamiliar subatomic (smaller than an atom) particle which interacts only very weakly with normal matter. If this is correct, billions of these particles will have passed via your body by the time you finish reading this article. Experiments buried deep underground may one day capture a number of these particles, finally solving the secret of what dark matter actually is.