When Keats proclaimed "A thing of beauty is a joy forever", he did not take into account the concept of entropy. Entropy will eventually send the nature he so eloquently describes to the path that all the living must take. "Dust to dust", as the Bible succinctly puts it.
Basically, entropy quantifies the quality of energy. It tells you if the energy available can do useful work or not, by measuring the amount of disorder in a system. It is continually increasing throughout the universe. An introduction, including its history, may be found at Bright Hub’s What is Entropy. One consequence of the theory, to use Robert Oppenheimer’s quote from the Bhagavad Gita, is its role as a "destroyer of worlds" via heat death. The universe will cease to change, because the entropy will be at a maximum.
A basic physics course teaches that the energy of the universe is constant; it cannot be created or destroyed, but it can be changed from one form to another. This concept was first put forth by the Scottish physicist Lord Kelvin, who was the first to develop the Kelvin as a temperature scale, and who also coined the term "thermodynamics". A refresher, including of how you can conduct your own experiment by rubbing your hands together, may be found at Bright Hub’s Conservation of Energy.
Lord Kelvin, combining the logic of no new energy sources with that of the relentlessness of entropy in light of the second law of thermodynamics, decided that there would be no more energy in the universe; all heat would diffuse evenly throughout, and all motion everywhere would cease. The temperature would be that of 0 kelvin or absolute zero.
German physician turned physicist Hermann von Helmholtz, following up on Lord Kelvin, coined the term "heat death" in 1854. He declared that the world would become of uniform temperature and "be condemned to a state of eternal rest". The idea of "the end of all physical phenomena" was developed by British physicist and engineer William Rankine, who is famed for his seminal work on steam engine theory such as the Rankine cycle.
When is the heat death of the universe supposed to occur, and what will happen to the Earth, the stars, and all living creatures when it happens? These questions will be addressed in part two.
Physics for Scientists and Engineers by Douglas Giancoli
Physics For Scientists and Engineers by Raymond Serway
Energy and Empire A Biographical Study of Lord Kelvin by Crosbie Smith and M. Norton Wise
Essential University Physics by Richard Wolfson
BBQ Fire by Avinmannn