Activity 4 The big bang

 BIG BANG

The Universe began in a Big Bang about 14 billion years ago. At that time, the whole universe was inside a very small bubble and it was very hot and dense.

Then it suddenly exploded. The universe was born: time, space and matter began with the Big Bang. In just a few seconds, the universe went from being smaller than a single atom to larger than a galaxy, and continued to grow. Today it is still expanding. As the Universe expanded and cooled, the energy was transformed into particles of matter and antimatter that were two opposite types of particles that destroyed each other. But something survived, the most stable particles called protons and neutrons began to form when the universe was a second old. Over the next three minutes, the temperature dropped below 1 billion degrees Celsius, it was cold enough for protons and neutrons to join, forming nuclei of hydrogen and helium. After 300,000 years, the universe had cooled to about 3,000 degrees. Atomic nuclei could eventually capture electrons to form atoms. The universe was filled with clouds of hydrogen and helium gas.