1. What is it?

The Big Bang theory describes how the Universe began in a rapid expansion about 13.7 billion years ago and has evolved since that time. It is thought that all of space was created in this first moment.

2. The first stars and galaxies formed about 560 million years after the Big Bang

Research from the European Space Agency’s Planck telescope lead scientists to believe that the first stars formed about 560 million years after the Big Bang. There is some evidence that stars may have formed even earlier.

3. A tiny, hot beginning

When the universe began, it was just hot, tiny particles mixed with light and energy. As the universe expanded and took up more space, it cooled down. The tiny particles then grouped together and formed atoms. Then those atoms grouped together and over LONG (100 million years) period of time, they came together to form stars and galaxies.

4. Based on many different observations

Scientists base the Big Bang theory on many different observations. The most important is the redshift of very far away galaxies. Redshift is when an object moves away from earth, it looks reddish because the movement stretches the wavelength. The reddish color occurs because red is the lowest wavelength on the visible spectrum. The more redshift there is, the faster the object is moving away. By measuring the redshift, scientists proved that the universe is expanding and can even work out how fast the object is moving.

5. There are still unknowns

The Big Bang Theory does not fully explain the true origin of the Universe, it is only based on the fact that a singularity (which was the Universe) was already there and that it expanded to form the modern Universe. What caused the singularity to expand, how it came into being, and what was before it is unknown.

6. The idea was first proposed by a Catholic priest 

The idea that would become the Big Bang Theory was first proposed by a Catholic priest named Georges Lemaitre, who called it his “hypothesis of the primeval atom.” Since then, scientists have built on his ideas and much evidence has arisen.

7. The glow of cosmic microwave background radiation

The glow of cosmic microwave background radiation, which is found throughout the universe, is thought to be a tangible remnant of leftover light from the big bang. The radiation is akin to that used to transmit TV signals via antennas. But it is the oldest radiation known and may hold many secrets about the universe’s earliest moments.

8.  Time had no meaning before the Big Bang

If the Big Bang was the beginning of time, then there was no universe before the Big Bang, since there could not be any “before” if there was no time.