It is believed by the scientific comunity that the universe had a specific time of origin. In the early 20th century, scientists observed that the entire universe was expanding. This led physicists to deduce that the universe started out in the finite past with a minuscule size.
The Big Bang theory tries to explain the origin and evolution of universe. According to the theory, 12 to 14 billion years ago, the universe as we see now, was only a few millimeters across and has expanded since then.
 Why should I be aware of it?
Realizing that the universe had a beginning, and awed by its vastness and its creations, people have wanted to know how the universe began. Is the scintific reason behind the origin of the universe acceptable to the theologists. Is it against the religion? Is there any proof of the theory?
 All about the big bang
The big bang theory states that the universe had a beginning. Its size is changing. The theory also links the origin of light and time to the big bang.
 What is the big bang?
Scientists and astronomers believe that about 14 billion years ago the universe began by expanding from an infinitesimal volume with extremely high density and temperature.
The universe was initially significantly smaller than even a pore on human skin. With the big bang, the fabric of space itself began expanding like the surface of an inflating balloon – matter simply rode along the stretching space like dust on the balloon's surface. The big bang is not like an explosion of matter in otherwise empty space; rather, space itself began with the big bang and carried matter with it as it expanded. The Universe grew from smaller than a single atom to bigger than a galaxy. And it kept on growing at a fantastic rate. It is still expanding today.
As the Universe expanded and cooled, energy changed into particles of matter and antimatter. These two opposite types of particles largely destroyed each other. But some matter survived. More stable particles called protons and neutrons started to form when the Universe was one second old.
 New form of matter
Until about thirty years ago, astronomers thought that the universe was composed almost entirely of this "baryonic matter", ordinary atoms. However, in the past few decades, there has been ever more evidence accumulating that suggests there is something in the universe that we can not see, perhaps some new form of matter.
 Fate of the universe
The evolution of the universe is determined by a struggle between the momentum of expansion and the pull (or push) of gravity. The current rate of expansion is measured by the Hubble Constant, while the strength of gravity depends on the density and pressure of the matter in the universe. If the pressure of the matter is low, as is the case with most forms of matter we know of, then the fate of the universe is governed by the density.
If the density of the universe is less than the critical density, then the universe will expand forever.
 Something new?
The universe began with an unimaginably enormous density and temperature. This immense primordial energy was the cauldron from where all life arose. Elementary particles were created and destroyed by the ultimate particle accelerator in the first moments of the universe.
There was matter and there was antimatter. When they met, they annihilated each other and created light. Somehow, it seems that there was a tiny fraction more matter than antimatter, so when nature took its course, the universe was left with some matter, no antimatter, and a tremendous amount of light. Today, there is more than a billion times more light than matter.
 Unanswered questions
- What types of matter and energy fill the universe? How much of each?
- How rapidly is the universe expanding today?
- How old is the universe today?
- What is the overall shape of the universe? Open, flat, closed, or otherwise?
- How is the expansion changing with time?
- What is the ultimate fate of the universe?
- The universe is 13.7 billion years old. 
- In 1951, the Catholic Church officially pronounced the big bang model to be in accordance with the Bible.
- Scientists believe that the first stars in the universe arose only about 400 million years after the Big Bang.
- The universe was initially significantly smaller than even a pore on our skin.
- We see the Sun not as it is now, but how it was eight minutes ago. (The Sun is eight light minutes away from the Earth). We see the nearby stars as they were several years ago. We see Andromeda, the nearest spiral galaxy as it was roughly 2.5 million years ago.
- The most distant objects that we see are the oldest objects that we can directly detect.
- Patricia A. Mondore, M.A. and Robert J. Mondore. A Very Big Bang
- Big Bang Cosmology
- Big bang machine 'absolutely safe'
- Evolutionary 'Big Bang' Created Florist's Paradise
- Big Bang: How Did the Universe Begin?