Writer C P Snow remarkedd in his book,' The Two Cultures and the Scientific Revolution', that it (SLTD)should be no less familiar to us than any of the works of Shakespeare.
Given that many people are ignorant of the works of the great bard, it's not a bad idea to mention this all important law of physics.

Developed during the 19th century, the laws of thermodynamics describe how quatities such as heat and energy of motion were shown to be forms of the same thing, namely energy. In terms of the Universe, the total amount of energy released by the big bang is a constant, it can never decrease, only change.

" The total amount of energy available in the Universe ( the ultimate isolated system) was a constant and one form could be transformed into another". This is the first law of thermodynamics.

The second law states that " The entropy (disorder) of an isolated system always tends to increase.

In 1854, Herman Von Helmholtz pointed out that as time elapsed, all energy would eventually be transformed into heat at a uniform temperature and all natural processes would cease". This is known as the concept of heat dissapation of energy.

In other words, all the energy in the universe cannot decrease but it can change, say whenever heat flows from a hot body to cold one. Entropy was further defined by Ludwig Boltzman in 1878. ' According to my definition, entropy depends on the probabilities of molecular arrangments. For example, if a state can has a very large number of different ways its molecules can be arranged, then it has a very large entropy. An egg falls to the floor and breaks. It is unlikely then to reform itself into its original shape. There it is then. Energy cannot flow by itself from a cold bodies to hot ones. Heat transference is a one way street, once scrambled, an egg cannot unscramble itself.

It is by this law that time is directed in which direction to flow.

Ian

REf : Introduction to Stephen Hawking by J P McVoy and Oscar Zarate, 1999, Icon Books.