What is Big Bang Theory?
We all should have studied it in our school days that there was nothing and suddenly a bang happened and the Universe born..
But the actual definition of Big Bang Theory is, 'The universe was in an initial singularity state in which all the matters & energies were in combined state. At some point the universe started to expand and cool. From that time, it started to act as per the known laws of physics to human kind'.
If you ask, "So prior to that point Universe doesn't exist?"
Then the answer will be "It is difficult to explain because the universe was acting beyond our understanding". So all our calculations & theories starting from the point at which the Universe started to expand from singularity.
At the beginning, Universe was dense and hot, so no formation was possible. Once the expansion started, it cooled eventually and the universe formation started in a way that particles formed. They combined and formed structures from atom to stars, galaxies and other mega structures.
What is the future?
The universe we see now, is in the same structure for millions of years with very minor changes. But after thousands of millions of years, the universe will further cool up and it will cause serious changes.. The observable universe will limited to the local galactic clusters. New stars won't form and existing stars will die. The mega structures will decompose and turn into the basic objects of matters. After some time, the matters may decompose.
Is this the end of Universe?
Some thoeries suggests that expansion may halt and reverse. Some theories suggests that quantum fields collapse and the forces, particles and structures take different form. But all these possibilities are likely to happen after several billion years.
We have seen the simple explanation of big bang theory. Please check my other post for more detailed explanation of Big Bang Theory.
We will see about the structures of Universe in my next post.