Everything in the universe has a beginning and an end, even the universe itself. It has a beginning and an end.
Many theories have been developed on how the universe born, the most famous one and commonly known is the Big Bang Theory.
But, How does one universe, come to an end?
Scientists have theorized things that affecting how our universe will end.
Those things are how much dark energy are in our universe, the overall shape of our universe and on the equation of state which determines how the dark energy density responds to the expansion of the universe.
Here's some theories on some fate of our universe
This scenario of the end of the universe is the result of continued expansion of the universe, where the temperature asymptotically approaches absolute zero.
In this case, the birth of a star in our universe will decrease and drop to zero as the fuel needed to form a star will be exhausted after a long period of time, around 10^12 to 10^14 years. The remaining star in our universe will slowly but surely run out of fuel too and died. With lack of stars in our universe, it will become more and more dark, until eventually, be dominated by black holes. Those black holes will also cease to exist due to hawking radiations until there are just cloud of photons and light particles and those will also eventually decays until there is nothing left. Unless . . ., theoretically, over infinite amount of time, there could be a spontaneous entropy decrease as a result of something called "Quantum Tunneling", leading in a new Big Bang.
The current rate of acceleration of our universe, also known as hubble constant is not big enough to destroy local structures in the universe, likes galaxies that held together by a strong gravitational force from their center self. However, the current rate are big enough to make them grow further away overtime. In this case, rate of acceleration keep increasing steadily overtime, it might be strong enough that gravity can't hold it anymore, our local structures like galaxies will be torn apart because the space between them is increasing, and then the stars, planet, black holes, and many other object in space will be destroyed, since their own gravity can't hold against the acceleration of the universe. This will keep going and going until eventually space itself accelerating faster than the speed of light, and even atoms would be destroyed. Because of that no particle will be able to interact with each other and the universe will become home of countless random particles that wander randomly without being able to do anything forever.
In both of above scenarios, gravity loses against dark energy and expansion of the universe keep increasing, while in this case, gravity wins!. If dark energy in our universe is less than we think or decrease, gravity will win and take everything together. The expansion of the universe will eventually slow down, stop, and going back to the way it was. All of the object in the universe will grow closer and closer appart, making the universe smaller and hotter. This objects like planets, stars, black holes, and many other will eventually merge into one giant black hole that contains the entire universe, until it collapsed and back to the way the universe started with the Big Bang
This scenario of the end of the universe state that, our universe has going on infinite cycle of birth and death, and reborn again. one possible cylcle might be The Cycle of Big Bang, and end with Big Crucnh and repeat. Or following the scenario of Big Freeze, a spontaneous drop in entropy could lead into a new Big Bang and repeat.