Why does the universe tend to disorder and chaos? When you see how scientists define disorder, the answer is obvious!
A disordered system is said to be in a state of high entropy. Entropy is just a measure of the number of ways that a system can arrange itself in a given state. There is only 1 way to arrange 8 coins so that they are all heads up, but many ways to arrange them so that there are 4 heads up and 4 tails up. If these coins are able to flip sides randomly, it is unlikely that they would ever arrive in the ordered, 8 heads up, state. Instead they would descend into disorder, towards the 4 heads up and 4 tails up state. Surprisingly, it is this march from order to disorder that gives time a sense of direction. Entropy gives rise to the 'arrow of time'.
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