Heat death of the universe

Thermal death (also entropic death) is one of the possible final states of the universe, in which there is no free energy to create and maintain life and others processes. In physical terms, the universe will have reached maximum entropy.

Origin of the hypothesis

The thermal death hypothesis is based on the second law of thermodynamics, which says that in an isolated system, entropy tends to increase. If the universe persists long enough, it will asymptotically reach a state in which energy would be distributed uniformly and, since there were no heat gradients, the last of the possible ways of transforming it would no longer be possible.

The idea was initially proposed by William Thomson, Lord Kelvin, who in 1851 theorized about the consequences of heat loss by Sadi Carnot in 1824 and Rudolf Clausius in 1865, but it was Hermann von Helmholtz who developed the idea of thermal death later.

In 1862, William Thomson published 'On the Age of the Heat of the Sun', an article where he reaffirmed his fundamental belief in the indestructibility of energy and the diffusion of heat, Thomson wrote:

The result would inevitably be a state of universal rest and death, if the universe is finite and is bound to obey existing laws. But it is impossible to conceive a limit to the extent of matter in the universe; and so science turned rather towards an endless progression, in an endless space, those actions that result from the transformation of the potential energy into palpable motion and therefore in heat, instead of a single finite mechanism, would work as a clock that would stop forever.

Cosmological theories

The probable consequences of this phenomenon are three, if the universe is not part of a multiverse that affects it in some way:

I.- Big Crunch: The dark energy will end and gravity will let all the celestial bodies get closer and closer until they form a single celestial mass, turning the universe into a kind of fireball.

II.- Big Rip: All celestial bodies will be consumed indefinitely until all star systems no longer exist, and the fabric of space-time is 'torn'.

III.- Alternative: The universe will continue to be a dark and cold place, without energy and matter.

Temperature of the universe (hot death vs cold death)

The "hot death" of the universe occurs when it reaches a state of maximum entropy. This occurs when all the energy has moved to places of lower energy, and the entire universe is in thermal equilibrium. Once this has happened, the flow of energy ceases.

This concept is very different from that commonly referred to as "cold death". The "cold death" of the universe occurs when it continues to expand forever. Due to this expansion, the universe becomes increasingly colder, and eventually becomes unable to support any life.

The opposite concept of "cold death" of the universe or "Big Rip" It is not that of the "hot death", but that of the "Big Crunch". The "Big Crunch" It occurs when the universe has so much density of matter that it contracts back into itself until it is reduced to a point. Due to this contraction, the universe becomes increasingly hotter and eventually also becomes incapable of supporting any life.