Activity 3: Big bang, the origin and the expansion of the Universe

There was a small stone very hot about 14 million years ago. The energy in the stone exploded and the galaxy was created. All this happened in one second. As the Universe expanded and cooled, energy splited in particles of matter and antimatter. These two opposite types of particles were largely destroyed, but something survived. More stable particles called protons and neutrons began to form when the Universe had a second. All this happened in one second.

Over the next three minutes, the temperature dropped below 1 billion degrees Celsius. It was now cool enough for the protons and neutrons to come together, forming hydrogen and helium nuclei. After 300.000 years, the Universe had cooled to about 3.000 degrees. Atomic nuclei could finally capture electrons to form atoms. The Universe filled with clouds of hydrogen and helium gas.