For millennia men have wondered whether the world as we know it will come to an end and if so, how the world will end. In ancient Judaism speculation about the world's end took the form of apocalypticism, the view that God will bring about the end of human history, exercising judgement upon the life of every person, and inaugurating His everlasting Kingdom. This apocalyptic viewpoint was taken up into early Christianity through its founder Jesus of Nazareth. The early Christians looked forward to the return of Christ at some unknown time in the future when he would inaugurate a new heaven and a new earth fit for eternal habitation. Here is how that event is described in the Apocalypse of John, the last book in the New Testament:
Then I saw a great white throne and him who was seated on it. From his presence earth and sky fled away, and no place was found for them. And I saw the dead, great and small, standing before the throne, and books were opened. Then another book was opened, which is the book of life. And the dead were judged by what was written in the books, according to what they had done. And the sea gave up the dead who were in it, Death and Hades gave up the dead who were in them, and they were judged, each one of them, according to what they had done. Then Death and Hades were thrown into the lake of fire. This is the second death, the lake of fire. And if anyone's name was not found written in the book of life, he was thrown into the lake of fire.
Then I saw a new heaven and a new earth, for the first heaven and the first earth had passed away, and the sea was no more. And I saw the holy city, new Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband. And I heard a loud voice from the throne saying, "Behold, the dwelling place of God is with man. He will dwell with them, and they will be his people, and God himself will be with them as their God. He will wipe away every tear from their eyes, and death shall be no more, neither shall there be mourning nor crying nor pain anymore, for the former things have passed away."—
Because of its commitment to apocalypticism, one of the major categories of Christian theology came to be Eschatology. From the Greek word
which means last or final, eschatology is the doctrine of the last things, including the return of Christ, the last judgement, and heaven and hell. For millennia eschatology remained the exclusive province of theology.
During the last half century all that has changed. Eschatology has now also become a branch of physics, and, yes, the very term
is the preferred nomenclature for this field of study. Physical eschatology is a sub-discipline of cosmology, which is the study of the large-scale structure and evolution of the universe. Cosmology subdivides into two parts: Cosmogony is the sub-discipline which studies the origin and past history of the universe. Eschatology, by contrast, is the sub-discipline which explores the future and final fate of the universe. Just as physical cosmogony looks back in time to retrodict the history of the cosmos based on traces of the past and the laws of nature, so physical eschatology looks forward in time to predict the future of the cosmos based on present conditions and laws of nature. The challenge for those interested in the interface between theology and science is how to arrive at an integrated perspective on the world's future adequate to the concerns of both theology and science.
The key to physical eschatology is the Second Law of Thermodynamics. About the middle of the nineteenth century, several physicists sought to formulate a scientific law that would bring under a general rule all the various irreversible processes encountered in the world. The result of their efforts is now known as the Second Law of Thermodynamics. As first formulated by Clausius, it stated that heat only flows of itself from a point of high temperature toward a point of low temperature; the reverse is never possible without compensation. But heat is only an instance of an even more general tendency toward levelling in nature; the same is true, for example, of gases and electricity. Without this general tendency toward levelling, life would be completely impossible. For example, because of such levelling, the air in the room never suddenly separates into oxygen at one end and nitrogen at the other. It is also why when we step into a bath we may be confident that the water will be pleasantly warm instead of frozen at one end and boiling at the other. It is easy to see why life would not be possible in a world where the Second Law of Thermodynamics did not hold.
The German physicist Ludwig Boltzmann deepened our understanding of the Second Law by showing that this tendency toward levelling is founded on the tendency of any system to pass from a less probable to a more probable state. According to Boltzmann, the probability of a state is a function of its order: more ordered states are less probable, and less ordered states are more probable. The most probable state is therefore a totally disordered state, that is, a state which is completely undifferentiated. Thus, the Second Law could be formulated: all systems have the tendency to pass from a more ordered to a less ordered state.
A third important step in the development of the Second Law was the realization that disorder is connected with entropy, or the measure of unusable energy: the greater the disorder the greater the entropy. This yields a third formulation of the law: all systems have the tendency to pass from a state of lower entropy into a state of higher entropy. In order to exlude the possibility of the system's leaking energy to its surroundings or acquiring energy from them, an additional stipulation is required: the system must be closed. This leads to a fourth formulation of the Second Law: spontaneously proceeding processes in closed systems are always attended by an increase in entropy. Thus, processes taking place in a closed system tend toward a state of equilibrium. The law in this form is virtually certain. To illustrate: the probability of all molecules in one litre of gas occupying only 99.99% of the volume instead of 100% is about 1:10
. For all practical purposes, therefore, the Second Law of Thermodynamics may be regarded as certain.