If we believe in the philosophy that everything that has a beginning has an end, then surely even the universe would come into that. In his book About Time, Paul Davies gives us a glimpse of the beliefs of our ancestors on what they thought about the existence of the universe and whether it is dying. It is impossible to separate scientific images of time from the cultural background that pervaded Europe during the Renaissance and the modern scientific era.
European culture has been strongly influenced by Greek philosophy and the religious systems of Judaism, Islam, and Christianity. The Greek legacy was the assumption that the world is ordered and rational, and can be understood through human reasoning: if so, then the nature of time can, in principle, be grasped by mortals.
From Judaism came the Western concept of time so central to the scientific world view. In contrast to the pervasive notion of time as cyclic, the Jews came to believe in linear time. A central tenet of the Jewish faith, subsequently inherited by both Christianity and Islam, was that of the historical process, whereby God’s plan for the universe unfolds according to a definite temporal sequence.
In this system of belief, the universe was created by God at a definite moment in the past, in a very different state from the one that exists today. The theological succession of events—creation, fall, redemption, judgement, resurrection—is paralleled by a divinely directed sequence of physical events—order out of primeval chaos, origin of the Earth, origin of life, origin of mankind, destruction and decay.
The concept of linear time carries with it the implication of an arrow of time, pointing from past to future and indicating the directionality of sequences of events. The origin of time’s arrow as a physical principle is still a curiously contentious scientific mystery. Scientists and philosophers have been sharply divided over the significance of the arrow of time. The conundrum, put crudely, boils down to this: is the universe getting better or worse? The Bible tells the story of a world that starts in a state of perfection—the Garden of Eden—and degenerates as a result of man’s sin. However, a basic component of Judaism, Christianity and Islam is a message of hope, of belief in personal betterment and the eventual salvation of mankind.
In the middle of the nineteenth century, physicists discovered the laws of thermodynamics, and it was soon realized that these implied a universal principle of degeneration. The so-called second law of thermodynamics is often phrased by saying that every closed system tends towards a state of total disorder or chaos. In daily life we encounter the second law in many familiar contexts, well captured by familiar sayings: It’s easier to break it than make it; there’s no such thing as a free lunch; Sod’s Law, Parkinson’s Law, etc. When applied to the universe as a whole, the second law implies that the entire cosmos is stuck fast on a one-way slide towards a final condition of total degeneration—i.e., maximum disorder—which is identified with the state of thermodynamic equilibrium.
One measure of the remorseless rise of chaos uses a quantity called “entropy,” which is defined to be, roughly speaking, and the degree of disorder in a system. The second law then states that in a closed system the total entropy can never decrease; at best it remains the same. Almost all natural changes tend to increase the entropy, and we see the second law at work all around us in nature. One of the most conspicuous examples is in the way that the sun slowly burns up its nuclear fuel, spewing heat and light irretrievably into the depths of space, and raising the entropy of the cosmos with each liberated photon.
Eventually, the sun will run out of fuel and cease to shine. The same slow degeneration afflicts all the stars in the universe. In the mid-nineteenth century, this dismal fate came to be known as the “cosmic heat death.” The thermodynamic “running down” of the cosmos represented a significant break with the concept of the Newtonian clockwork universe. Instead of regarding the universe as a perfect machine, physicists now saw it as a gigantic heat engine slowly running out of fuel. Perpetual-motion machines were found to be unrealistic idealizations, and the alarming conclusion was drawn that the universe is slowly dying. Science had discovered pessimistic time, and a new generation of atheistic philosophers, led by Bertrand Russell, wallowed in the depressing inevitability of cosmic doom.