Everything we see in this world has a cause including the universe. If the universe was eternal, it would not have a beginning, nor need a cause.
Here are ten points that show that the universe began to exist and therefore is not eternal.
Now, all that’s left is to discover what, or who, caused it.
God, The Beginning and the Big Bang: 10 Quick Points [Updated]
1) If the universe has only been in existence for a finite amount of time, then it is rational to believe that the universe began to exist. If the big bang theory is true, it provides strong evidence that our universe has only existed for a finite amount of time and, therefore, that our universe began to exist.