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Big Bang

The Universe expands after the Big BangThe Universe expands after the Big BangScientists believe that the Universe began life in a single momentous event. This was an incredibly hot, dense explosion called the Big Bang, which took place about 13.7 billion years ago. It is hard to imagine that before the Big Bang, no matter or energy existed. There was no such thing as time. During this explosion, all matter, energy, space—even time itself—were created in an instant. It is said that in the first trillion-trillion-trillionth of a second of its existence, the Universe grew one hundred million times in size. It has continued to expand at an incredible rate ever since.

A history of the UniverseA history of the Universe

Universe timeline

  • Millionths of a second old The first subatomic particles form.
  • One second old Protons and neutrons, the subatomic particles that form the nuclei of atoms, start to form.
  • Three minutes old The temperature drops below 1 billion °C. Protons and neutrons come together to form the nuclei of hydrogen and helium atoms.
  • 300,000 years old The first atoms, those of hydrogen and helium, are formed when atomic nuclei finally "capture" electrons.
  • 500 million years old The first galaxies and stars are formed.
  • 4 billion years old The Milky Way Galaxy starts to form.
  • 9 billion years old The Solar System comes into existence.

Formation of matter

In the first few millionths of a second, the particles that make up atoms, the building blocks of all matter, were formed. It took hundreds of thousands of years for the first atoms, those of the gases hydrogen and helium, to come together. By this time, the searing heat of the Big Bang had cooled, space had expanded and the gases began to spread out. Gradually, however, gravity drew the gases together, leaving vast regions of empty space in between.

Animation showing the formation of a galaxyAnimation showing the formation of a galaxyClick to play video

Formation of galaxies

The amount of energy actually used at the Big Bang was tiny. If converted to matter it would be the equivalent of a bag of sugar.

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