1. The Universe
A journey through time

2. The Big Bang Sometime between 13 and 20 billion years ago
The theory that best explains the current universe is the Big Bang theory. This theory states that, in the beginning, the universe was all in one place. All of its matter and energy were squished into an infinitely small point, a singularity.

4. Big Bang cont’d
Something unknown caused the universe to explode, and thus began the expansion that we see today.
The early universe was small, so everything happened very quickly compared to the timescales on which events happen for the present universe.
At the start, the universe was very small and dense. This stage was called the primordial fireball.
For the first second, only elementary particles, such as protons, neutrons, and electrons, could exist. But the universe quickly cooled and expanded.

5. Big Bang cont’d
For about the next 500,000 years, electromagnetic radiation (light) was the most important thing in the universe and hence this time was known as the radiation era.
When the universe had cooled to the point where the simplest atoms (hydrogen) could form, radiation no longer dominated and matter took over. (matter era)

6. Cosmic radiation
The Big Bang theory predicts that the early universe was a very hot place and that as it expands, the gas within it cools. Thus the universe should be filled with radiation that is literally the remnant heat left over from the Big Bang, called the “cosmic microwave background radiation”, or CMB.

7. Cosmic radiation
In the 1960's a startling discovery was made by accident. A pair of scientists at Bell Laboratories detected some annoying background noise using a special low noise antenna. The strange thing about the noise was that it was coming from every direction and did not seem to vary in intensity at all. They had discovered the Cosmic Microwave Background Radiation.

8. Universe beginnings
In 1927, the "Belgian priest Georges Lemaître" was the first to propose that the universe began with the explosion of a primeval atom.
His proposal came after observing the red shift in distant nebulas by astronomers to a model of the universe based on relativity.
Years later, Edwin Hubble found experimental evidence to help justify Lemaître's theory. He found that distant galaxies in every direction are going away from us with speeds proportional to their distance.

9. The big bang was initially suggested because it explains why distant galaxies are traveling away from us at great speeds. The theory also predicts the existence of cosmic background radiation (the glow left over from the explosion itself). The Big Bang Theory received its strongest confirmation when this radiation was discovered in 1964 by Arno Penzias and Robert Wilson, who later won the Nobel Prize for this discovery.

10. See article