Eventhough we didn't know what exactly happened at the moment of Big Bang . It is a widely accepted theory that has been a beacon of light to our existance. From nothingness to something and it all happened with a gigantic explosion. Todays Doomsday Scenario Big Crunch is the quite opposite of the Big Bang from everything to nothingness.
What is Big Crunch Theory ?
Well According to this unique theory appearently our universes expansion is not limitless and the Gravity is slowing this. Before I continue further I want to briefly mention about a term first used by Albert Einstein called Dark Energy. It is a mysterious quantitity basicly makes up three fourts of the universe. However the scientists have no clue about this matter and how , it operates.
Obviously Dark Energy is still a huge mystery but we all thought that gravitional forces were slowing the expension of universe , However when scientists observe that our universe is even expanding in more in a faster rate they started to think it is because of the famous Dark Energy.
So what we learned ? University is expanding widely. So according to this Big Crunch theory because of this huge expension and the gap created by it gravitional forces is going to fade and eventually our universe expanding will being to halt and it will being to contract , therefore all the planets , stars and galaxies will gather in the center of the universe to create the ultimate blackhole. basicly it is going to be a reset for our universe.
Doomsday Scenario
So our universe is going to expand expand and expand , but sadly even the cosmic fabric of the universe won't handle this much expansion and eventually it will pop up like a baloon or something. It will create a big rip or big crunch and it will devour and destroy all the universe and break the fabric of time and universe.
Good part is we don't have to worry about these kind of stuff because it is still beyond our comprehension so you shouldn't lose your sleep because of Big Rip or Big Crunch and it is a better way of ending for our universe instead of getting eaten by a space giant called Galactus. It all started with a Big Bang and it will all end with a Big Crunch