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The heat death of the universe, also known as the Big Chill or Big Freeze,^[1] is a conjecture on the ultimate fate of the universe, which suggests the universe would evolve to a state of no thermodynamic free energy and would therefore be unable to sustain processes that increase entropy. Heat death does not imply any particular absolute temperature; it only requires that temperature differences or other processes may no longer be exploited to perform work. In the language of physics, this is when the universe reaches thermodynamic equilibrium (maximum entropy).

The heat death of the universe, also known as the Big Chill or Big Freeze, If the cosmological constant is zero, the universe will approach absolute zero temperature over a very long timescale. However, if the cosmological constant is positive, as appears to be the case in recent observations, the temperature will asymptote to a non-zero positive value, and the universe will approach a state of maximum entropy in which no further work is possible.^:§VIA With only very diffuse matter remaining, activity in the universe will have tailed off dramatically, with extremely low energy levels and extremely long timescales. Speculatively, it is possible that the universe may enter a second inflationary epoch, or assuming that the current vacuum state is a false vacuum, the vacuum may decay into a lower-energy state.^:§VE It is also possible that entropy production will cease and the universe will reach heat death.^:§VID Another universe could possibly be created by random quantum fluctuations or quantum tunneling in roughly [math]\displaystyle{ 10^{10^{10^{56}}} }[/math] years. Over vast periods of time, a spontaneous entropy decrease would eventually occur via the Poincaré recurrence theorem, thermal fluctuations, and fluctuation theorem. Such a scenario, however, has been described as "highly speculative, probably wrong, [and] completely untestable". Sean M. Carroll, originally an advocate of this idea, no longer supports it.

宇宙的热死，也被称为大寒或大冻---- 如果宇宙学常数为零，宇宙将在很长一段时间内接近绝对零度。然而，如果宇宙学常数是正的，就像最近观测到的那样，温度将渐近到一个非零的正值，宇宙将接近一个最大熵的状态，在这种状态下不可能做进一步的工作。由于只剩下非常分散的物质，宇宙中的活动将急剧减弱，能量水平极低，时间尺度极长。推测地说，宇宙可能会进入第二个暴胀时期，或者假设当前的真空状态是假真空，真空可能会衰变为低能状态。也有可能产生熵将停止，宇宙将达到热死。另一个宇宙可能是由随机的量子涨落或量子穿隧效应在大约10 ^ {10 ^ {56}} </math > 年内创造出来的。在大量的时间里，自发的熵减少最终会通过庞加莱始态复现定理、热涨落和涨落定理发生。然而，这种情况被描述为“高度投机，可能是错误的，并且完全不可测试”。最初支持这一观点的肖恩 · m · 卡罗尔不再支持这一观点。

If the topology of the universe is open or flat, or if dark energy is a positive cosmological constant (both of which are consistent with current data), the universe will continue expanding forever, and a heat death is expected to occur,^[2] with the universe cooling to approach equilibrium at a very low temperature after a very long time period.

The hypothesis of heat death stems from the ideas of Lord Kelvin, who in the 1850s took the theory of heat as mechanical energy loss in nature (as embodied in the first two laws of thermodynamics) and extrapolated it to larger processes on a universal scale.

Concept

The concept of the heat death of the universe is based on the observation that the gravitational potential energy of the universe, also known as rest mass that is stored mostly in baryons, self‑gravitationally shrinks and heats up to ever higher temperatures. Consequently, the ever‑smaller and ever‑hotter baryons "evaporate", with an exponential acceleration, into the seemingly expanding ambient space as photons, so that eventually the universe will consist of zero‑frequency photons:

If the rest mass decreases by Δm₀, the kinetic energy E = c²Δm₀ is produced. The same thing is true if we replace production of kinetic energy E by production of radiant energy E. Continuing this line of argument, one can envisage the possibility that the whole rest mass m of a body could be converted into energy. Then the energy E = m₀c² would be produced and the whole rest mass of the body would disappear.

—International Encyclopedia of Unified Science Vol. 1, nos. 6–10, University of Chicago Press, 1955, p. 460

Although mechanical energy is indestructible, there is a universal tendency to its dissipation, which produces throughout the system a gradual augmentation and diffusion of heat, cessation of motion and exhaustion of the potential energy of the material Universe.

—Thomson, William. On the Age of the Sun’s Heat Macmillan's Magazine, 5 March 1862, pp. 388–93

The exponential acceleration of baryons' evaporation has been described by Arthur Eddington:

All change is relative. The universe is expanding relatively to our common material standards; our material standards are shrinking relatively to the size of the universe. The theory of the "expanding universe" might also be called the theory of the "shrinking atom". <...>

Let us then take the whole universe as our standard of constancy, and adopt the view of a cosmic being whose body is composed of intergalactic spaces and swells as they swell. Or rather we must now say it keeps the same size, for he will not admit that it is he who has changed. Watching us for a few thousand million years, he sees us shrinking; atoms, animals, planets, even the galaxies, all shrink alike; only the intergalactic spaces remain the same. The earth spirals round the sun in an ever‑decreasing orbit. It would be absurd to treat its changing revolution as a constant unit of time. The cosmic being will naturally relate his units of length and time so that the velocity of light remains constant. Our years will then decrease in geometrical progression in the cosmic scale of time. On that scale man's life is becoming briefer; his threescore years and ten are an ever‑decreasing allowance. Owing to the property of geometrical progressions an infinite number of our years will add up to a finite cosmic time; so that what we should call the end of eternity is an ordinary finite date in the cosmic calendar. But on that date the universe has expanded to infinity in our reckoning, and we have shrunk to nothing in the reckoning of the cosmic being.

We walk the stage of life, performers of a drama for the benefit of the cosmic spectator. As the scenes proceed he notices that the actors are growing smaller and the action quicker. When the last act opens the curtain rises on midget actors rushing through their parts at frantic speed. Smaller and smaller. Faster and faster. One last microscopic blurr of intense agitation. And then nothing.

—Eddington, Arthur. The Expanding Universe CUP, 1933, pp. 90–92

Category:Physical cosmology
类别: 物理宇宙学

Category:Thermodynamic entropy

类别: 熵

Category:Doomsday scenarios

分类: 末日情景

After the evaporation of all baryons, the resultant bath of zero‑frequency photons, indistinguishable from empty space, will condense into new protons, each miles across, which will undergo another 13.8‑billion‑year‑long exponentially accelerating shrinkage and evaporation. And so ad infinitum:

Category:1851 in science

类别: 1851年的科学

Category:Ultimate fate of the universe
类别: 宇宙的终极命运

This page was moved from wikipedia:en:Heat death of the universe. Its edit history can be viewed at 热寂/edithistory

↑ WMAP – Fate of the Universe, WMAP's Universe, NASA. Accessed online July 17, 2008.

↑ {{Cite book Max Planck wrote that the phrase "entropy of the universe" has no meaning because it admits of no accurate definition. More recently, Walter Grandy writes: "It is rather presumptuous to speak of the entropy of a universe about which we still understand so little, and we wonder how one might define thermodynamic entropy for a universe and its major constituents that have never been in equilibrium in their entire existence." According to Tisza: "If an isolated system is not in equilibrium, we cannot associate an entropy with it." Buchdahl writes of "the entirely unjustifiable assumption that the universe can be treated as a closed thermodynamic system". According to Gallavotti: "... there is no universally accepted notion of entropy for systems out of equilibrium, even when in a stationary state." Discussing the question of entropy for non-equilibrium states in general, Lieb and Yngvason express their opinion as follows: "Despite the fact that most physicists believe in such a nonequilibrium entropy, it has so far proved impossible to define it in a clearly satisfactory way." In Landsberg's opinion: "The third misconception is that thermodynamics, and in particular, the concept of entropy, can without further enquiry be applied to the whole universe. ... These questions have a certain fascination, but the answers are speculations, and lie beyond the scope of this book." 马克斯 · 普朗克写道，“宇宙的熵”这个短语没有任何意义，因为它不承认有准确的定义。最近，Walter Grandy 写道: “我们仍然对宇宙的熵知之甚少，我们想知道如何定义一个宇宙及其主要成分的熵，而这些成分在整个存在过程中从未处于平衡状态。”蒂萨说: “如果一个孤立的系统不处于平衡状态，我们就不能把熵和它联系起来。”布赫达尔写道: “宇宙可以被视为一个封闭的热力学系统，这是完全不合理的假设。”。根据 Gallavotti 的说法: “对于失去平衡的系统，没有普遍接受的熵的概念，即使是在定态中。”在讨论一般非平衡态的熵问题时，Lieb 和 Yngvason 表达了他们的观点如下: “尽管大多数物理学家相信存在这样的非平衡熵，但迄今为止已经证明不可能以一种明显令人满意的方式来定义它。”兰兹伯格认为: “第三个误解是，热力学，特别是熵的概念，不需要进一步探究就可以应用于整个宇宙。...这些问题有一定的吸引力，但答案都是推测，超出了本书的范围。” | title = Death from the Skies! | last = Plait A 2010 analysis of entropy states, "The entropy of a general gravitational field is still not known", and "gravitational entropy is difficult to quantify". The analysis considers several possible assumptions that would be needed for estimates and suggests that the observable universe has more entropy than previously thought. This is because the analysis concludes that supermassive black holes are the largest contributor. Lee Smolin goes further: "It has long been known that gravity is important for keeping the universe out of thermal equilibrium. Gravitationally bound systems have negative specific heat—that is, the velocities of their components increase when energy is removed. ... Such a system does not evolve toward a homogeneous equilibrium state. Instead it becomes increasingly structured and heterogeneous as it fragments into subsystems." 2010年对熵状态的分析表明，“一个普通引力场的熵仍然不为人知” ，“引力熵很难量化”。该分析考虑了几个可能的假设，这些假设对于估计来说是必要的，并且表明可观测宇宙的熵比之前想象的要多。这是因为分析得出结论，超大质量黑洞是最大的贡献者。李 · 斯莫林更进一步说: “人们早就知道，引力对于防止宇宙进入热平衡十分重要。引力束缚系统具有负的比热，也就是说，当能量消失时，其组分的速度增加。...这样的系统不会演化到均匀的平衡状态。相反，随着它分解成子系统，它变得越来越结构化和异构化。” | first = Philip This point of view is also supported by the fact of a recent experimental discovery of a stable non-equilibrium steady state in a relatively simple closed system. It should be expected that an isolated system fragmented into subsystems does not necessarily come to thermodynamic equilibrium and remain in non-equilibrium steady state. Entropy will be transmitted from one subsystem to another, but its production will be zero, which does not contradict the second law of thermodynamics. 最近在一个相对简单的封闭系统中实验发现了稳定的非平衡稳态，这也支持了这一观点。可以预期的是，一个分裂成子系统的孤立系统不一定会达到热力学平衡并保持非平衡的稳定状态。熵将从一个子系统传递到另一个子系统，但是它的产出将为零，这与热力学第二定律并不矛盾。 | publisher = Viking Adult | isbn = 978-0-670-01997-7 | publication-date = 16 October 2008 | pages = 259 | author-link = Phil Plait | title-link = Death from the Skies! | year = 2008 }}

[1] WMAP – Fate of the Universe, WMAP's Universe, NASA. Accessed online July 17, 2008.

[DftS-2] {{Cite book Max Planck wrote that the phrase "entropy of the universe" has no meaning because it admits of no accurate definition. More recently, Walter Grandy writes: "It is rather presumptuous to speak of the entropy of a universe about which we still understand so little, and we wonder how one might define thermodynamic entropy for a universe and its major constituents that have never been in equilibrium in their entire existence." According to Tisza: "If an isolated system is not in equilibrium, we cannot associate an entropy with it." Buchdahl writes of "the entirely unjustifiable assumption that the universe can be treated as a closed thermodynamic system". According to Gallavotti: "... there is no universally accepted notion of entropy for systems out of equilibrium, even when in a stationary state." Discussing the question of entropy for non-equilibrium states in general, Lieb and Yngvason express their opinion as follows: "Despite the fact that most physicists believe in such a nonequilibrium entropy, it has so far proved impossible to define it in a clearly satisfactory way." In Landsberg's opinion: "The third misconception is that thermodynamics, and in particular, the concept of entropy, can without further enquiry be applied to the whole universe. ... These questions have a certain fascination, but the answers are speculations, and lie beyond the scope of this book." 马克斯 · 普朗克写道，“宇宙的熵”这个短语没有任何意义，因为它不承认有准确的定义。最近，Walter Grandy 写道: “我们仍然对宇宙的熵知之甚少，我们想知道如何定义一个宇宙及其主要成分的熵，而这些成分在整个存在过程中从未处于平衡状态。”蒂萨说: “如果一个孤立的系统不处于平衡状态，我们就不能把熵和它联系起来。”布赫达尔写道: “宇宙可以被视为一个封闭的热力学系统，这是完全不合理的假设。”。根据 Gallavotti 的说法: “对于失去平衡的系统，没有普遍接受的熵的概念，即使是在定态中。”在讨论一般非平衡态的熵问题时，Lieb 和 Yngvason 表达了他们的观点如下: “尽管大多数物理学家相信存在这样的非平衡熵，但迄今为止已经证明不可能以一种明显令人满意的方式来定义它。”兰兹伯格认为: “第三个误解是，热力学，特别是熵的概念，不需要进一步探究就可以应用于整个宇宙。...这些问题有一定的吸引力，但答案都是推测，超出了本书的范围。” | title = Death from the Skies! | last = Plait A 2010 analysis of entropy states, "The entropy of a general gravitational field is still not known", and "gravitational entropy is difficult to quantify". The analysis considers several possible assumptions that would be needed for estimates and suggests that the observable universe has more entropy than previously thought. This is because the analysis concludes that supermassive black holes are the largest contributor. Lee Smolin goes further: "It has long been known that gravity is important for keeping the universe out of thermal equilibrium. Gravitationally bound systems have negative specific heat—that is, the velocities of their components increase when energy is removed. ... Such a system does not evolve toward a homogeneous equilibrium state. Instead it becomes increasingly structured and heterogeneous as it fragments into subsystems." 2010年对熵状态的分析表明，“一个普通引力场的熵仍然不为人知” ，“引力熵很难量化”。该分析考虑了几个可能的假设，这些假设对于估计来说是必要的，并且表明可观测宇宙的熵比之前想象的要多。这是因为分析得出结论，超大质量黑洞是最大的贡献者。李 · 斯莫林更进一步说: “人们早就知道，引力对于防止宇宙进入热平衡十分重要。引力束缚系统具有负的比热，也就是说，当能量消失时，其组分的速度增加。...这样的系统不会演化到均匀的平衡状态。相反，随着它分解成子系统，它变得越来越结构化和异构化。” | first = Philip This point of view is also supported by the fact of a recent experimental discovery of a stable non-equilibrium steady state in a relatively simple closed system. It should be expected that an isolated system fragmented into subsystems does not necessarily come to thermodynamic equilibrium and remain in non-equilibrium steady state. Entropy will be transmitted from one subsystem to another, but its production will be zero, which does not contradict the second law of thermodynamics. 最近在一个相对简单的封闭系统中实验发现了稳定的非平衡稳态，这也支持了这一观点。可以预期的是，一个分裂成子系统的孤立系统不一定会达到热力学平衡并保持非平衡的稳定状态。熵将从一个子系统传递到另一个子系统，但是它的产出将为零，这与热力学第二定律并不矛盾。 | publisher = Viking Adult | isbn = 978-0-670-01997-7 | publication-date = 16 October 2008 | pages = 259 | author-link = Phil Plait | title-link = Death from the Skies! | year = 2008 }}

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