Most astronomers believe that the universe began about 15 billion years ago in a fiery explosion called the Big Bang .

In one instant, all the space, time, matter and energy in the universe came into being as a tiny speck, then started to expand rapidly. As the universe got bigger and cooler, the force of gravity started to take hold.

At the moment of the Big Bang

A fraction of a second after the Big Bang, the infant universe went through a sudden growth spurt, called inflation. In far less than a billionth of a second, the universe grew faster than at any other time in its history. Inflation only lasted an instant, and then the universe slowed down to the rate of expansion we see today.

After one second

As the universe continued to expand and cool, protons, neutrons and electrons condensed out of the background energy, especially in areas where the energy was slightly "denser."

After 100 seconds

Protons and neutrons combined to form helium nuclei. Hydrogen nuclei, which are simply protons, already existed. In less than two minutes, all the sub-atomic elements that exist today had been formed.

After 300 000 years

By this time, the universe had cooled enough for electrons to combine with atomic nuclei, thereby forming atoms. These atoms slowly gravitated into vast strand-shaped clouds, from which the galaxies would soon emerge.

After one billion years

Clouds of hydrogen and helium began "clumping" under the force of gravity. As the clouds grew denser, early galaxies-called protogalaxies-began to take shape. These protogalaxies grew bigger and bigger. Some of them started spinning and flattening out into disk-like shapes. Others stayed more or less spherical as they grew.

Eventually, these primal galaxies gathered enough mass for stars to ignite within them, and for the first time, the universe took on the appearance we see today.
Canadian Heritage Information Network
Australian Museums & Galleries Online, Australia; Centre of the Universe; Gemini Observatory, Hawaii; Glenbow Museum; The Manitoba Museum; National Research Council Canada; Planétarium de Montréal

© Canadian Heritage Information Network, 2003

Teachers' Centre Home Page | Find Learning Resources & Lesson Plans