Entropy: Arrow of Time
But is entropy (disorderliness) of the universe increasing? Book Conceptual Physics by Paul G. Hewitt defines second law of thermodynamics as "Heat of itself never flows from a cold object to a hot object" What is temperature? Temperature is a measure of the average translational kinetic energy of the molecules in a substance. What is heat? The energy transferred from one object to another because of a temperature difference between them is called heat. So, in theory, heat will travel from hot object to cold object till the average translational kinetic energy of both the object becomes same. Now, look at the complete universe. If second law of thermodynamics would have been the only rule for changing the average translational kinetic energy, then the universe would be in equilibrium i.e. if you take any object in the universe, it would have the same average translational kinetic energy. Here I assume that universe is not expanding. If universe would be ex