Here is step 1 of the Kalaam Cosmological Argument for the existence of God.
Did the Universe have Beginning (or no beginning)?
A. The Big Bang theory Refutes the Eternal Universe (part 16)
B. The 2nd law of thermodynamics Refutes the Eternal Universe
The next proof the universe had a beginning comes the 2nd law of thermodynamics or the law of entropy. This law says that in a closed universe the finite amount of energy is winding down, moving towards a time when all energy will be expended. If we spin a ball on a table what we find is that it has a finite or limited amount of energy that was applied to spin the ball. The spinning ball will soon stop; it has run out of energy. In a similar fashion the universe with its limited amount of energy, is going to wind down to where there is no energy left.
Another illustration of the 2nd law of thermodynamics utilizes a hot cup of coffee. Over time the coffee cools and the heat moves outward into the room. Soon the temperature of the coffee and the room will be equal. The same goes for the universe. Heat is moving outward from stars and is being uniformly distributed throughout the universe. Eventually the limited amount of heat energy of the stars throughout the universe will run out and suffer what is called, “Heat death.” L. Barnet said this, “The universe is progressing toward an ultimate heat death or, as it is technically defined, a condition of maximum entropy. When the universe reaches this state some billions of years from now, all the processes of nature will cease. All space will be the same temperature… There will be no light, no life, no warmth–nothing but perpetual and irrevocable stagnation…and there is no way of avoiding this destiny!”
If the universe was eternal, all the heat energy would have been utilized an infinite amount of time ago. If this is true then we should currently be at heat death. All the energy should have been used up an eternity ago. Since energy exists today we can conclude the universe is not eternal. If the universe is not eternal, it must have had a beginning. Both the big bang and 2nd law of thermodynamics refute an eternal universe.
 Barnet, L., The Universe and Dr. Einstein, New American Library, 1957 pg. 102-3