While predictions of the future can never be absolutely certain, a projected course for the farthest future events may be sketched out based on present scientific understanding in various fields, if only in the broadest strokes. All predictions of the future of the Earth, the Solar System and the Universe must account for the second law of thermodynamics, which states that entropy, or a loss of the energy available to do work, must increase over time. Stars must eventually exhaust their supply of hydrogen fuel and burn out. Eventually, matter itself will come under the influence of radioactive decay, as even the most stable materials break apart into subatomic particles. The infinite future potentially allows for the occurrence of a number of massively improbable events, such as the formation of a Boltzmann brain. Many questions about the far future are still unresolved, such as whether humans will become extinct, whether protons decay or whether the Earth will be destroyed by the Sun's expansion into a red giant (illustration pictured). (Full list...)