深奥的简洁

• 目送飞鸿

  2020-05-21
  This is compelling evidence that the biological and physical components of our planet are part of a single network which operates in a self-organized way (Lovelock uses the expression self-regulating) to maintain conditions that are broadly suitable for the existence of life, but which undergoes fluctuations on all scales (including Ice Age-Interglacial rhythms, and mass extinctions) analogous to the fluctuations that occur in the sandpile model. In a real sense, the Earth is home to a single living network, and the existence of that network (Gaia) would be easily apparent to any intelligent life on Mars capable of applying the Lovelock test and looking for signs of entropy reduction.
• 目送飞鸿

  2020-05-21
  So the link between oceans and land resulting from the production of DMS by marine algae operates as a two-way street, to the benefit of life in both places.
• 目送飞鸿

  2020-05-21
  The implication of all this is that microscopic life-forms in the oceans play a key role in controlling the climate of the Earth. In a natural feedback process, if the algae became more active, cloud cover over the oceans would increase, there would be less sunlight available for photosynthesis, and biological activity would decline; but if biological activity declines, less DMS is released by the algae, fewer clouds form, so there is more sunlight available for photosynthesis and life thrives. It is just like the kind of self-organizing feedback we see at work in Daisyworld, and the tendrils of the network extend into many aspects of life on Earth.
• 目送飞鸿

  2020-05-21
  In the language of the previous chapter, he is saying that the behaviour of life on Earth alters the physical landscape (where ‘physical’ includes things like the composition of the atmosphere) as well as the biological landscape, and that both these changes affect the overall fitness landscape, with feedback a key component of the interactions.
• 目送飞鸿

  2020-05-21
  It came to Lovelock, ‘suddenly, just like a flash of enlightenment’, that for the atmosphere of the Earth to stay in this seemingly stable state for hundreds of millions of years ‘something must be regulating the atmosphere and so keeping it at its constant composition. Moreover, if most of the gases came from living organisms, then life at the surface must be doing the regulation.’ Without pausing to think it through further, he blurted out the insight to his companions at the time, a NASA colleague called Dian Hitchcock, and another visitor to JPL, the astronomer Carl Sagan. This was the seed from which the idea of Gaia, the Earth as a self-regulating system, grew (the name was suggested, incidentally, by one of Lovelock’s neighbours in England, the writer William Golding).
• 目送飞鸿

  2020-05-21
  He suggested that what was needed was an experiment that could look for the general attributes of life, rather than specific kinds of life, and, when challenged to explain what kind of experiment could do that, replied that what was needed was an experiment to look for entropy reduction. As Lovelock appreciated, and as we have seen earlier in this book, living systems characteristically bring local order to systems, making entropy ‘run backwards’ as long as they have an external source of energy to feed on....The best way to look for entropy reduction processes at work on Mars would be to measure the chemical composition of its atmosphere. If there were no life on Mars, the gases in the atmosphere would be in a state of thermodynamic and chemical equilibrium, dominated by stable compound...
• 目送飞鸿

  2020-05-19
  The implication is that the economy is a system that follows the same laws as the occurrence of earthquakes (or traffic jams), and that large events (in this case, things like stock market crashes, such as the crash of October 1987) can happen out of the blue, as a consequence of small triggers....Classical economics is based on principles very similar to those of classical thermodynamics, and deals with systems (economies) that are close to equilibrium....Modern economists like Arthur are dealing with dynamic, changing systems, in which positive feedbacks are involved and through which a form of energy (in this case, money) flows. Put like that, the story is familiar. Thanks to feedback in particular, economies are actually self-organizing systems on the edge of chaos, with all that t...
• 目送飞鸿

  2020-05-19
  The Universe cannot, in principle, be predicted in all its detail; but, equally, time cannot, in principle, be reversed.
• 目送飞鸿

  2020-05-19
  Even if, as Laplace thought, the Universe is entirely deterministic and the whole future is contained within its present state, there is no way at all to predict or know the future, except by watching the Universe evolve. Whether or not we have free will, the Universe behaves as if we have free will, which is really all that matters. The Universe is ignorant of its own future, and is its own fastest simulator.
• 雪人快跑

  2018-08-25
  近似碎性的自我类似是生物组织的普遍特质，这也是体内工作能被有效率地执行的原因。
• 雪人快跑

  2018-08-25
  生物细胞DNA中所储存的遗传讯息，常被视为建造个体的“蓝图”；但这个比喻不很恰当。真正的蓝图应该很复杂，它刻画生物系统中的所有细节以及彼此连接的方式。就好比蛋糕食谱，它不告诉你蛋糕完成时的模样（更不用说是做好的蛋糕上每个葡萄干的位置了），只告诉你“混合以下几种材料，再用若干温度，烘烤若干时间”。
• 雪人快跑

  2018-08-25
  即使如拉普拉斯所认为，宇宙是决定式的，未来的宇宙决定于当下状态，而除了看着它演变，我们也完全无法预测未来。宇宙使我们看似拥有自由意志，但我们是否真的拥有自由意志，才是问题的根本。宇宙对自己的未来似乎并不在意，它只是对自身最快速的模拟器。
• 雪人快跑

  2018-08-25
  这故事还有个情节。就目前所知，我们有这样大的卫星——月亮——最佳解释是在太阳系形成早期，有一个接近火星大小的小星体，因为混沌作用脱离小行星带撞上地球，而溅起的熔化物质在太空中形成月亮。
• 凯文怎么了

  2012-05-26
  我们今天所知道的热力学第二定律有许多不同的表达方式，在1852年首度清楚地提出这个理论的事英国乌鲁学家威廉汤姆森，他把重点放在‘散失（Dissipation）’的观念上。虽然大自然的运作可以被看成一个将热转换为功（或运动）的巨大机器，总会有一些热在这个过程中散失；不是真的消失，只是扩散到整个宇宙中，使其整体温度升高一些。这个主张脱离了当时能量守恒定律（热力学第一定律）的概念，因为这样一来，虽然宇宙的总能量不变，‘可使用能量’却不断减少。这促使物理学家必须想出方法量化一个封闭系统（整个宇宙）中可使用的能量，才能界定其数值并用方程式处理。因此，德国的克劳修斯在1860年代中期提出了‘熵（entropy）的观念’。
• 盗三

  2021-03-18
  但当我终于知道混沌是怎么一回事时，我还是大吃一惊。我的理解是：重点只在于某些系统（“系统”包含的范围可以很广，比如摆荡的钟摆、太阳系或水龙头的滴水规律）对于初始条件非常敏感，因此初始“那一刹那”的少许差异，会造成截然不同的结果。此外，还有“反馈（ feedback），反馈使得系统会影响自身的行为。这一切看起来太完美了，简单得令人难以置信！因此当我请教朋友吉米・拉夫洛克（ Jim Lovelock）时，我问道：“是否混沌和复杂所探讨的一切，只是建立于两个简单的概念之上——系统对初始状态的敏感以及回馈？”他回答：“一点几也没错，全都包在里面。”
• 盗三

  2022-12-11
  当然，动物不见得一定会有图案，即使相关的生化机制确实存在。这种机制可以被关掉，我们从进化的角度很容易看出，比如像北极熊就只有单一的白色外表。但当图案显现时，由表面大小产生不同图案的关联性，我们可以从猫科动物的尾巴上找到一个十分有趣的例子。对于基本上是柱状的尾巴，图案可能是斑点或环绕尾巴的圆环。但像美洲豹，即使开始时以斑点覆盖，到了尾巴末端，尾尖上形成的仍是条纹图案，这与模型所预测的条纹出现在较小表面，斑点出现在较大表面的结果一致。这个模型有个重要特质，动物表面图案并非取决于成年动物的大小与形状，而取决于图灵式的过程发生时胚胎的大小与形状。当然，大象胚胎会比老鼠胚胎大；但胚胎大小的重要性可以从两种斑马——草原斑马（Equus burchelli）与格利威斑马（Equus grevyi）——的不同条纹的对比中得到完美的印证。前者有较少、较宽的条纹，虽然成年动物体型差不多，但将两种斑马放在一块我们就很容易看出差别。20世纪0年代J.B.L.巴德（J.B.L.Bard）计算了两种斑马的条纹数目，并考虑了生长过程中图案被扭曲的方式，他宜称，草原斑马的条纹必然在胚胎受精21天时被决定，而格利威斑马的图案则是在35天时被决定。这早在莫瑞运用图灵效果建立数学模型之前便为人所知，但这个差别完美地呼应了模型预测。基因与环境（先天与后天）的这种戏剧性结合，在2002年初第一只克隆猫诞生时就充分显现了出来。因为具有多种颜色的动物身上的图案与色彩，取决于基因遗传以及子宫内的条件（例如发育胚胎接收的营养），所以即便这两只动物有相同的DNA，小猫皮毛上的图案仍然和母猫的并不完全相同。
• 目送飞鸿

  2020-05-19
  Turing showed that there are systems which cannot be ‘compressed’ algorithmically, and whose most compact representations are themselves – one of the key concepts we encountered, from another direction, in our earlier discussion of chaos. In particular, as we have seen, the shortest description of the Universe is the Universe itself.
• 目送飞鸿

  2020-05-19
  In a sense, classical thermodynamics pretends that time does not exist....Classical thermodynamics also assumes that there is no flow of energy – specifically, heat – through a system....Dissipation of energy is an essential feature of non-equilibrium thermodynamics, giving us another way of referring to the flow of energy through a system, as a dissipative process. These are also referred to as open systems, because (unlike the hypothetical closed box of gas beloved by the nineteenth-century thermodynamic pioneers) they are not sealed off from the world at large. It is in closed systems that we encounter time reversibility and Poincaré recurrences; in open systems we encounter irreversibility and an arrow of time.
• 目送飞鸿

  2020-05-16
  Away from equilibrium, a flow of energy can, under the right circumstances, create order spontaneously. This is a crucial insight into our own existence, since there is no denying that we are ordered creatures, and there is overwhelming evidence that the Universe began in a state of much less order.
• 目送飞鸿

  2020-05-16
  Life, of course, seems to defy this process, by creating order and structure out of disordered (or at least, less ordered) materials. A plant builds its structure, and may make beautiful flowers, out of carbon dioxide, water, and a few traces of other chemicals. But it only does so with the aid of sunlight, energy from an outside source.