The second law of thermodynamics has been expressed in many ways, but it basically means that every ordered system will break down into a disordered state in a process called entropy. This principle is credited to the French scientist Sadi Carnot, who in 1824 showed that there is an upper limit to the efficiency of conversion of heat to work in an engine. This principle eventually led to the concept of the asymmetric arrow of time, which states that once an event has taken place, it cannot be reversed. Generally, we observe entropy at work every day. A spilled cup of coffee cannot be made to refill, and you cannot put back a broken egg.
However, if the second law of thermodynamics was valid in all conditions, the universe as we know it could not exist. Cosmologists have difficulty explaining the behavior of the observable universe and the working of entropy. Many of them ignore the problem by saying that galaxies and stars have evolved from a low state of entropy, which means a more ordered state, and that contradicts what we see. An image of the cosmic background radiation that represents low energy photons that have decayed from the Big Bang is a random assembly of energies, which confirms that the Big Bang was a highly disordered system, a soup of energetic photons. The early universe was in a state of maximum entropy. It could not become more disordered.
But as the universe expanded and cooled, this chaotic system gradually became more ordered, giving rise to fundamental forces, quarks, protons, neutron, and electrons, which coalesced into elements, molecules, and dust that coalesced into stars and galaxies, all highly ordered systems. Granted, once these organized systems formed, they became subject to entropy. Cosmologists and theoretical physicist talk learnedly about the second law of thermodynamic and the arrow of time, but they have failed to explain the tendency of chaotic systems to become ordered.
Gradually, some understanding of this process is beginning to emerge from the theory of chaos, first advocated by Edward Lorenz in 1961. In common usage, ‘chaos’ means ‘a state of disorder’, which neatly explains the early universe. Such systems are extremely sensitive to minute influence in initial conditions, and in the early universe, gravitational fluctuations and variations in matter and energy, set the parameters that gave rise to more ordered states, or levels of low entropy, in apparent violation of the second law of thermodynamics.
Will this apparent contradiction be eventually resolved? Probably, but it will take the unification of quantum mechanics and the general theory of relativity that deals with gravity.