U.S. Department of Energy

Pacific Northwest National Laboratory

Glossary

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The Big Bang

The Big Bang gave birth to all the matter and energy that exists in the universe today. The Big Bang set the universe in motion and initiated its expansion about 13.7 billion years ago.

The Visible Universe

The Visible Universe includes everything that can be “seen” by the electromagnetic radiation it emits. This includes not just human-visible matter like stars and planets, but also sources such as the cosmic microwave background and astronomical radio, x-ray and gamma ray sources. Dark Matter and Dark Energy are explicitly excluded from the Visible Universe.