Heat Death, Cosmic

The cosmic heat death of the universe is a prediction that, as everything tends to move from order to chaos, the universe will eventually “run down” like an old clock. The second law of thermodynamics states that entropy tends to increase in an isolated system. The arrow of time points to the fact that all heat in the universe will die eventually. This is borne out by the everyday observation that things tend to move from a higher energy state to a lower energy state. High energy states can also be manifested as more highly organized collections of atoms. Any solid will gradually disperse over time. Given enough time, even all the atoms of the universe will break down.

As various physical phenomena have been studied and understood it has become apparent that over time everything moves to this lower-energy, more dispersed state. from the universe's first moments as a single high-energy point of all matter, it is moving toward dispersal as the energy that binds everything runs down. Scientists currently believe we live in an open universe and that everything will continue over time to expand infinitely in all directions. According to current understandings of particle physics and cosmology, in around 10100 years the universe will move to a low-energy, steady state of photons and leptons, dispersed through infinite space.

The death will happen in three phases. First the universe will become dark as the stars go out. The death will follow the pattern of increasing entropy as the energy level and matter density of the universe drop to a level at which galaxies and stars cease to form, around 10 to 100 trillion years from now. Some 14 trillion years after that, the last of the long-lived stars (red dwarves) will go out.

The second phase will be the decay of the complex structure of the material universe. At a point some 1014 (1,000 trillion) years from now, the visible structure of the universe will begin to degenerate at its lower levels; planets will begin to decay as they leave their orbits as the result of an accumulated weakening of the gravitational force. These changes will be followed approximately 1015 years later by degeneration at the highest levels; galaxies will begin to decay as stars leave their orbits. The final level of visible structural disorder will not take place until around 1040years in the future when matter itself begins to break down. All matter is made of elementary particles, chiefly protons, neutrons, and electrons [Page 637]in various combinations. The predicted half-life of protons is 1036 years, which means that by 1040years from now virtually no protons will exist.

The last phases of the universe will be visible only at the subatomic level. When more than 10100 years have passed, the last remaining macroscopic structures will disappear as the last black holes evaporate into photons and leptons. The universe will be at an absolute minimum temperature and a featureless sea of subatomic particles subject only to random quantum fluctuations.