The Universe: Beginnings

The Story of Creation (According to the Big Bang)

In the beginning (some 15 billion years ago), the universe exploded in one cataclysmic "Big Bang." For an instant, only energy existed as the tremendous heat of the explosion (1 x 1032 degrees) unified everything. As space erupted, matter, energy, and time itself were created. In the first seconds of time, the early universe expanded and cooled to 100 billion degrees, and protons, neutrons, and electrons began to take form. Within moments, as temperatures plunged to 1 billion degrees above zero, small atomic nuclei began to take shape as protons and neutrons began to interact. After 300,000 years, temperatures in the universe had dropped below 3,000 degrees and neutral atoms were formed as electrons combined with the atomic nuclei.

Gravity and the other fundamental forces were also created in this explosion and they began to cause the early atoms to pull together into dense clouds called nebulae. Over time, nebulae collapsed into massive objects called stars, which bathed the universe in light. As the tremendous pressure of a star's own gravity squeezes the atoms inside of it together, stars fuse light elements (such as hydrogen and helium) into heavier ones (carbon, nitrogen, oxygen, etc.) (see our Nuclear Chemistry module for more information). Over billions of years, a star eventually exhausts its nuclear fuel and ends its life in a cataclysmic explosion, called a supernova. This process spreads the star's matter back into space and begins the cycle anew.

As the early universe developed, the stars were drawn together into large clusters called galaxies. One such cluster, called the Milky Way galaxy, began to form approximately 10 billion years ago. Much like other galaxies around it, the Milky Way contains some 100 billion stars spiraling around its center. Then, approximately 5 billion years ago, a new star called the sun was born in this galaxy.

Figure 1: The Sun

image ©NASA/JPL/Caltech

In its early years, the sun drew in gas and dust from nearby space. Some of this material began to spin around the early sun, forming a circling disc. Over time, dust and gases in this disc began to clump together into larger objects that eventually formed planets circling around the sun.

Nine planets were born in this solar system, each at a different distance from the sun and with different characteristics. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto each circle the sun in distinct orbits, as the following link clarifies.

Interactive Animation:
The Nine Planets

Anthony Carpi, Ph.D. “The Universe” Visionlearning Vol. ASTR-1 (1), 2003.

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