EXPLORE: The Big Bang (BrainPop)
This book will explain the expansion of the universe, and how it led to the Big Bang Theory. It will also describe what happened and what the universe was like right after the Big Bang.
3. Big Bang (BrainPop)
A cluster of galaxies. Taken by the Hubble telescope. Image courtesy of rmforall@comcast.net/Flickr. Public domain.
The discovery that the universe is expanding told astronomers something about how the universe might have formed. Before this discovery, there were many ideas about the universe, most of them thinking of the universe as constant. Once scientists learned that the universe is expanding, the next logical thought is that at one time it had to have been smaller. The Big Bang Theory was proposed by Lemaitre in 1927 and quickly confirmed by Hubble's discovery of the red shift in 1929.
The Big Bang Theory is the most widely accepted scientific explanation of how the universe formed. This theory posits that the universe emerged from an enormously dense and hot state 13.7 billion years ago. The Big Bang Theory is based on Hubble's law redshift of distant galaxies. The redshift gives the speed that objects are moving away from us and this basically measures the current rate of expansion of the universe. That expansion rate is used to calculate back to a time the universe was in one spot and began expanding. The age of the universe depends on an accurate measure of our current rate of expansion; the currently accepted value is a speed 65 kilometers per second per Megaparsec. Extrapolated into the past, these observations show how the Universe has expanded from a state in which all matter and energy in the Universe was at an immense temperature and density and squeezed into a very small volume.