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The Second Law is also known as the Law of Entropy, which is a complicated way of saying that nature tends to bring things to disorder.

That is, with time, things naturally fall apart. You car falls apart; your house falls apart; your body falls apart. But if the universe is becoming less ordered, then where did the original order come from?

Astronomer Robert Jastrow compares the universe to a wound-up clock. If a wind-up clock is running down, then someone must have wound it up.

This aspect of the Second Law also tells us that the universe had a beginning. Since we still have some order left – just like we have some usable energy left – the universe cannot be eternal, because if it were, we would have reached complete disorder or entropy by now.

As we conclude our discussion of this valuable piece of evidence, Arthur Eddington characterizes this law perfectly. He states, ” The Law of Entropy increases- the Second Law of Thermodynamics- holds, I think, the supreme position among the laws of nature. If someone points out to you that your pet theory of the universe with Maxwell’s equations – then so much for Maxwell’s equations. If it is found to be contradicted by observation, these experiments do bungle things sometimes. But if your theory is found to be against the Second Law of Thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.”

The next piece of evidence we will speculate is the fact that the universe is expanding.

How does the expanding universe prove a beginning?