Everything about Heat Death Of The Universe totally explained
The
heat death is a possible
final state of the universe, in which it has "
run down" to a state of no
thermodynamic free energy to sustain
motion or
life. In
physical terms, it has reached maximum
entropy. The hypothesis of a universal heat death stems from the 1850s ideas of
William Thomson (Lord Kelvin) who extrapolated the
theory of heat views of
mechanical energy loss in
nature, as embodied in the first two
laws of thermodynamics, to universal operation.
Origins of the idea
The idea of heat death stems from the
second law of thermodynamics, which states that
entropy tends to increase in an
isolated system. If the universe lasts for a sufficient time, it'll
asymptotically approach a state where all
energy is evenly distributed. In other words, in nature there's a tendency to the
dissipation (energy loss) of
mechanical energy (motion); hence, by extrapolation, there exists the view that the mechanical movement of the universe will run down in time due to the second law. The idea of heat death was first proposed in loose terms beginning in 1851 by
William Thomson, who theorized further on the mechanical energy loss views of
Sadi Carnot (1824),
James Joule (1843), and
Rudolf Clausius (1850). Thomson’s views were then elaborated on more definitively over the next decade by
Hermann von Helmholtz and
William Rankine.
History
The idea of heat death of the universe derives from discussion of the application of the first two
laws of thermodynamics to universal processes. Specifically, in 1851
William Thomson outlined the view, as based on recent experiments on the dynamical
theory of heat, that “heat isn't a substance, but a dynamical form of mechanical effect, we perceive that there must be an equivalence between mechanical work and heat, as between cause and effect.”
In 1852, Thomson published his “On a Universal Tendency in Nature to the Dissipation of Mechanical Energy” in which he outlined the rudiments of the
second law of thermodynamics summarized by the view that mechanical motion and the energy used to create that motion will tend to dissipate or run down, naturally. The ideas in this paper, in relation to their application to the age of the
sun and the dynamics of the universal operation, attracted the likes of
William Rankine and
Hermann von Helmholtz. The three of them were said to have exchanged ideas on this subject. In 1862, Thomson published the article “On the age of the sun’s heat” in which he reiterated his fundamental beliefs in the indestructibility of energy (the
first law) and the universal dissipation of energy (the
second law), leading to diffusion of heat, cessation of motion, and exhaustion of
potential energy through the material universe while clarifying his view of the consequences for the universe as a whole. The key paragraph is:
In the years to follow both Thomson’s 1852 and the 1865 papers, Helmholtz and Rankine both credited Thomson with the idea, but read further into his papers by publishing views stating that Thomson argued that the universe will end in a “heat death” (Helmholtz) which will be the “end of all physical phenomena” (Rankine).
Temperature of the universe
In a "heat death", the temperature of the entire universe would be very close to
absolute zero. Heat death is, however, not quite the same as "cold death", or the "
Big Freeze", in which the universe simply becomes too cold to sustain life due to continued
expansion, though the result is quite similar. For a "heat death" to occur,
proton decay must take place.
Current status
Inflationary cosmology suggests that in the early universe, before cosmic expansion, energy was uniformly distributed, and thus the universe was in a state superficially similar to heat death. However, the two states are in fact very different: in the early universe, gravity was a very important force, and in a gravitational system, if energy is uniformly distributed,
entropy is quite low, compared to a state in which most matter has collapsed into
black holes. Thus, such a state isn't in
thermal equilibrium, and in fact there's no
thermal equilibrium for such a system, as it's thermodynamically unstable. However, in the heat death scenario, the energy density is so low that the system can be thought of as non-gravitational, such that a state in which energy is uniformly distributed is a
thermal equilibrium state, for example, the state of maximal entropy.
The final state of the universe depends on the assumptions made about its
ultimate fate, and these assumptions have varied considerably over the late
20th century and early
21st century. In a
"closed" universe that undergoes recollapse, a heat death is expected to occur, with the universe approaching arbitrarily high temperature and maximal entropy as the end of the collapse approaches. In an
"open" or "flat" universe that continues expanding indefinitely, a heat death is also expected to occur, with the universe cooling to approach absolute zero temperature and approaching a state of maximal entropy over a very long time period. There is dispute over whether or not an expanding universe can approach maximal entropy; it has been proposed that in an expanding universe, the value of maximum entropy increases faster than the universe gains entropy, causing the universe to move progressively farther away from heat death. Finally, some models of
dark energy cause the universe to expand in ways that result in some amount of usable energy always being available, preventing the universe from ever reaching a state of maximum entropy. The expectation of the scientific community
as of 2007 is that the universe will continue expanding indefinitely.
The fate of sapient life in a universe approaching heat death is speculative, and again depends on the assumptions made. It has been proposed that in a collapsing universe, there's enough usable energy to perform an arbitrarily large amount of computation before the collapse completes. This scenario is called the
Omega point, and it would theoretically allow a society that practices
mind uploading to experience an arbitrarily large amount of subjective time in simulated realities. In an expanding universe, it has been proposed that some mechanism would exist to allow sapient life to continue processing information indefinitely. This proposal is called the
final anthropic principle. However, the expectation among the majority of scientists is that the heat death of the universe will bring an end to the ability to perform information processing, and hence an end to any form of sapient life.
Timeline for heat death
The Degenerate Age, from 1014 to 1040 years
Galaxy and star formation ceases: 1014 years
Stellar formation stops, leaving matter to decay over a very long period of time. The hydrogen fuel used for
fusion by stars will be eventually depleted, leaving all matter in the Universe in a compact state populated by the following objects after all stars burn out:
Planets fall or are flung from orbits: 1015 years
Over time, the
orbits of planets decay due to
gravitational radiation or the planets are ejected from their local systems by gravitational perturbations.
Stars fall or are flung from orbits: 1016 years
The same scattering effect happens to stars and their remnants within galaxies, leaving mostly scattered stellar debris and
supermassive black holes.
An estimated half of protons decay: 1036 years
If estimates of the
half-life of
protons are correct, then one-half of all the free-floating matter in the Universe has been converted into
gamma radiation and
leptons through
proton decay.
All protons decay: 1040 years
If estimates on the
half-life of protons (10
36 years) are correct, then protons (and nucleonic
neutrons as well) will undergo roughly 10,000 half-lives by the time the universe is 10
40 years-old. To put this into perspective, there are an estimated 10
80 protons currently in the Universe. This means the proton's numbers will be slashed in half 10,000 times by the time it's 10
40 years-old. Hence, there will be roughly ½
10,000 (approximately 5 × 10
–3011) as many protons remaining as there are today; that is,
zero protons remaining in the Universe at the end of the Degenerate Age. Effectively, all matter would be contained within black holes, which are immune to proton decay, and
leptons.
The Black Hole Age, from 1040 years to 10100 years
Black holes dominate: 1040 years
Black holes continue to evaporate via
Hawking radiation, but this process is very slow.
Black holes disintegrate: 10100 years
Few—if any—black holes remain; virtually all matter is now converted into
photons.
See also
1019 seconds for times further than 317 billion years into the future.
Ultimate fate
The Dark Age, from 10100 years until 10150 years
All Black Holes now Disintegrated: 10150 years
The remaining black holes evaporate: first the small ones, and then the
supermassive black holes. All matter that used to make up the stars and galaxies has now degenerated into photons and
leptons.
The Photon Age, 10150 years and Beyond
The Universe Achieves Low-Energy State: 101000 years and beyond »
The Universe now reaches an extremely low-energy state. What happens after this is speculative. It's possible a
Big Rip event may occur far off into the future, or the Universe may settle into this state forever, achieving true heat death. Extreme low-energy states imply that localized
quantum events become major macroscopic phenomena rather than negligible microscopic events because even unimaginably small perturbations would make the biggest difference in this era, so there's no telling what may happen to space or time. It is perceived that the laws of "macro-physics" will break down, and the laws of "quantum-physics" will prevail.
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