In the ancient times, philosophers all over the world thought that space above them is vast and never changing. And like all ancient ideology, it got cremated in 1929, when Edwin Hubble found out that all the galaxies in the universe are moving away from us. According to me, it was the most important breakthrough in history of science only after ‘The Discovery of Atoms’. This became a law known as the Hubble’s law. Galactic matter moving away from us implied only to one thing: the universe we live in is expanding.
If the universe is expanding, then there must be a state, where all the matter and energy is concentrated at one point (this is more of a logical statement, than a fact. A balloon can only expand if it is shrunk). This was the basic idea of The Big Bang.
Characteristic Of Universe At Time Of Big Bang:
- Big bang has no place 0f origin. It is because the space itself was created at the time of big bang. So if someone ask “where did big bang take place?”, you should answer “It took place everywhere”. It is because everything was at same place at the time of big bang.
- At the time of big bang, universe was in lowest possible state of entropy. It was time when everything was governed by unified field theory. Read the reference link to know more detail.
- If we measure the temperature at time of big bang, it would turn out to be 1023 kelvin. As the universe expanded temperature dropped and universe cooled down.
- The first force ever created was gravity. You might wonder that how could gravity be produced when the matter itself was in form of energy. The energy at that time was in form of matter wave (like electron, photon etc). So gravity was the first force that came into existence.
- Universe’s expansion was because of dark energy which at that point of time was lowest in percentage (but enough to take everything apart). As the arrow of time moved, the percentage composition of dark energy grew. That is why universe today is expanding at an accelerated rate.
Here are 2 important reference links