Will the universe end in a Big Crunch or a Big Rip?

[whiteholes]

How do you think our universe will end like? I think it would be the Big crunch! One evidence is that the amount of mass in stars divided by the total amount of mass in the universe is nonzero. After some length of time, any given star will convert too much hydrogen into helium (or heavier elements) to continue nuclear fusion. From this we conclude that in unit time, the amount of hydrogen converted into helium by a given star divided by the star's mass is nonzero. Combining this with the earlier statement, we conclude that the amount of hydrogen converted into helium by stars as a whole divided by the mass of the universe is nonzero. There is no known process that can return heavier elements to hydrogen in the necessary quantities, and any would probably violate the second law of thermodynamics. Therefore, the amount of time needed for stars to convert all of the hydrogen in the universe into helium is finite, and it will never change back. After this, only heavier-element-burning stars will exist (and these will die when they hit iron, an event known as the heat death of the universe). This hasn't happened yet, so either the universe is of finite age, it has undergone major changes in its history, or there exists some highly exotic process (for which no direct evidence exists) that produces hydrogen to keep it going.


So it is possible it will end in a Big Crunch! The time graph of our universe would be something like a bell shape that repeats itself. Getting larger after every Big bang.

 

[AlphaNumeric]

One evidence is that the amount of mass in stars divided by the total amount of mass in the universe is nonzero. After some length of time, any given star will convert too much hydrogen into helium (or heavier elements) to continue nuclear fusion. From this we conclude that in unit time, the amount of hydrogen converted into helium by a given star divided by the star's mass is nonzero. Combining this with the earlier statement, we conclude that the amount of hydrogen converted into helium by stars as a whole divided by the mass of the universe is nonzero.

Why is this evidence? You're just saying 'Stars make up a certain percentage of the universe's mass' and 'Hydrogen makes up a certain percentage of the stars, and this percentage is shrinking'.

This hasn't happened yet, so either the universe is of finite age

The entire 'big bang theory' revolves around the universe being of finite age (about 13~14 billion years).

There is evidence from supernova observations in other galaxies that the universe's expansion is accelerating. This is part of the reason for the 'dark energy' theories which have appeared in recent years.