|
什么是生命？
对于这个问题，如果请文学家和诗人来回答，回答一定是浪漫的。
但是科学家只能依据科学理论来回答这个问题。 他们根据热力学第一和第二定论清楚地阐述了生命的科学定义。生物体与内燃机本来没有区别；前者依赖食物维持生命，后者则需要燃料来发动运行。
物理学的理论和实验结果证明：自然界的过程一般是熵增的过程。但是科学家发现，生命体却是一个熵减的过程。于是生命有了科学的定义：一个熵减的系统。或者说：熵减是生命的特征。
比如，从一般的意义上可以这样来理解：生命体从环境中得到能量(食物与阳光)。这种能量物理上称为自由能。生命体吸收这部分能量而实现细胞的生长与分裂。然后再把吸收的同等能量释放给环境。细胞的生长与分裂是一种从无序到有序列的规则过程 (比如胚胎从不定型长出规则的人体和器官)。这种从比较无序到有序的过程无疑是熵减的。
我们在外星寻找生命时，就可以通过熵减现象来找到生命的蛛丝马迹。
我们一起来看看科学家是如何来定义生命的，很有趣呢！
文章来自： http://en.wikipedia.org/wiki/Entropy_and_life
Entropy and life
In 1910, American historian Henry Adams printed and distributed to university libraries and history professors the small volume A Letter to American Teachers of History proposing a theory of history based on the second law of thermodynamics and the principle of entropy.[1][2] The 1944 book What is Life? by Nobel-laureate physicist Erwin Schroedinger served largely to stimulate this research. In this book, Schroedinger states that life feeds on negative entropy, or negentropy as it is sometimes called. Recent writings have utilized the concept of Gibbs free energy to elaborate on this issue。
Origin
In 1863, Rudolf Clausius published his noted memoir "On the Concentration of Rays of Heat and Light, and on the Limits of its Action" wherein he outlined a preliminary relationship, as based on his own work and that of William Thomson, between his newly developed concept of entropy and life. Building on this, one of the first to speculate on a possible thermodynamic perspective of evolution was the Austrian physicist Ludwig Boltzmann. In 1875, building on the works of Clausius and Kelvin, Boltzmann reasoned:“ The general struggle for existence of animate beings is not a struggle for raw materials – these, for organisms, are air, water and soil, all abundantly available – nor for energy which exists in plenty in any body in the form of heat, but a struggle for entropy, which becomes available through the transition of energy from the hot sun to the cold earth. ”
Early views
In 1876, American civil engineer Richard Sears McCulloch, in his Treatise on the Mechanical Theory of Heat and its Application to the Steam-Engine, which was an early thermodynamics textbook, states, after speaking about the laws of the physical world, that "there are none that are established on a firmer basis than the two general propositions of Joule and Carnot; which constitute the fundamental laws of our subject." McCulloch then goes on to show that these two laws may be combined in a single expression as follows:
S = dQ/τ
where
S = entropy
dQ = equals a differential amount of heat passed into a thermodynamic system
τ = absolute temperature
McCullen then declares that the applications of these two laws, i.e. what are presently known as the first law of thermodynamics and the second law of thermodynamics, are innumerable. He then states:
“ When we reflect how generally physical phenomena are connected with thermal changes and relations, it at once becomes obvious that there are few, if any, branches of natural science which are not more or less dependent upon the great truths under consideration. Nor should it, therefore, be a matter of surprise that already, in the short space of time, not yet one generation, elapsed since the mechanical theory of heat has been freely adopted, whole branches of physical science have been revolutionized by it. ”
McCulloch then gives a few examples of what he calls the “more interesting examples” of the application of these laws in extent and utility. The first example he gives, is physiology wherein he states that “the body of an animal, not less than a steamer, or a locomotive, is truly a heat engine, and the consumption of food in the one is precisely analogous to the burning of fuel in the other; in both, the chemical process is the same: that called combustion.” He then incorporates a discussion of Lavoisier’s theory of respiration with cycles of digestion and excretion, perspiration, but then contradicts Lavoisier with recent findings, such as internal heat generated by friction, according to the new theory of heat, which, according to McCullen, states that the “heat of the body generally and uniformly is diffused instead of being concentrated in the chest”. McCullen then gives an example of the second law, where he states that friction, especially in the smaller blooded-vessels, must develop heat. Without doubt, animal heat is thus in part produced.” He then asks: “but whence the expenditure of energy causing that friction, and which must be itself accounted for?
To answer this question he turns to the mechanical theory of heat and goes on to loosely outline how the heart is what he calls a “force-pump”, which receives blood and sends it to every part of the body, as discovered by William Harvey, that “acts like the piston of an engine and is dependent upon and consequently due to the cycle of nutrition and excretion which sustains physical or organic life.” It is likely, here, that McCulloch was modeling parts of this argument on that of the famous Carnot cycle. In conclusion, he summarizes his first and second law argument as such:“ Everything physical being subject to the law of conservation of energy, it follows that no physiological action can take place except with expenditure of energy derived from food; also, that an animal performing mechanical work must from the same quantity of food generate less heat than one abstaining from exertion, the difference being precisely the heat equivalent of that of work. ”
What is life?
Later, building on this premise, in the famous 1944 book What is Life?, Nobel-laureate physicist Erwin Schroedinger theorizes that life, contrary to the general tendency dictated by the Second law of thermodynamics, decreases or maintains its entropy by feeding on negative entropy.[3] In a note to What is Life?, however, Schr?dinger explains his usage of this term:
“ Let me say first, that if I had been catering for them [physicists] alone I should have let the discussion turn on free energy instead. It is the more familiar notion in this context. But this highly technical term seemed linguistically too near to energy for making the average reader alive to the contrast between the two things. ”
This is what is argued to differentiate life from other forms of matter organization. In this direction, although life's dynamics may be argued to go against the tendency of second law, which states that the entropy of an isolated system tends to increase, it does not in any way conflict or invalidate this law, because the principle that entropy can only increase or remain constant applies only to a closed system which is adiabatically isolated, meaning no heat can enter or leave. Whenever a system can exchange either heat or matter with its environment, an entropy decrease of that system is entirely compatible with the second law.[4] The common justification for this argument, for example, according to renowned chemical engineer Kenneth Denbigh, from his 1955 book The Principles of Chemical Equilibrium, is that "living organisms are open to their environment and can build up at the expense of foodstuffs which they take in and degrade."[4]
In 1964, James Lovelock was among a group of scientists who were requested by NASA to make a theoretical life detection system to look for life on Mars during the upcoming space mission. When thinking about this problem, Lovelock wondered “how can we be sure that Martian life, if any, will reveal itself to tests based on Earth’s lifestyle?” [5] To Lovelock, the basic question was “What is life, and how should it be recognized?” When speaking about this puzzling issue with some of his colleagues at the Jet Propulsion Laboratory, he was asked, well what would you do to look for life on Mars? To this Lovelock replied：“ I’d look for an entropy reduction, since this must be a general characteristic of life. ”
Thus, according to Lovelock, to find signs of life, one must look for a “reduction or a reversal of entropy.”
Gibbs free energy
In recent years, the thermodynamic interpretation of evolution in relation to entropy has begun to utilize the concept of the Gibbs free energy, rather than entropy. This is because biological processes on earth take place at roughly constant temperature and pressure, a situation in which the Gibbs free energy is an especially useful way to express the second law of thermodynamics. The Gibbs free energy is given by:
dG = dH-TdS
The minimization of the Gibbs free energy is a form of the principle of minimum energy, which follows from the entropy maximization principle for closed systems. Moreover, the Gibbs free energy equation, in modified form, can be utilized for open systems when chemical potential terms are included in the energy balance equation. In a popular 1982 textbook Principles of Biochemistry by noted American biochemist Albert Lehninger, it is argued that the order produced within cells as they grow and divide is more than compensated for by the disorder they create in their surroundings in the course of growth and division. In short, according to Lehninger, "living organisms preserve their internal order by taking from their surroundings free energy, in the form of nutrients or sunlight, and returning to their surroundings an equal amount of energy as heat and entropy."[6]
In 1998, noted Russian physical chemist Georgi Gladyshev, in his book Thermodynamic Theory of the Evolution of Living Beings, argues that evolution of living beings is governed by the tendency for quasi-equilibrium, semi-closed, hierarchical living systems to evolve in the direction that tends to minimize the Gibbs free energy of formation of each structure.[7][8] Variations of the Gibbs function of formation of a thermodynamic system at any stage of the evolution, for instance ontogenesis and phylogenesis, such as a social system, according to Gladyshev, "can be calculated by means of thermodynamic methods." Gladyshev calls this a form of sociological thermodynamics.
Similarly, according to the chemist John Avery, from his recent 2003 book Information Theory and Evolution, we find a presentation in which the phenomenon of life, including its origin and evolution, as well as human cultural evolution, has its basis in the background of thermodynamics, statistical mechanics, and information theory. The (apparent) paradox between the second law of thermodynamics and the high degree of order and complexity produced by living systems, according to Avery, has its resolution "in the information content of the Gibbs free energy that enters the biosphere from outside sources."[9]
References
Adams, Henry. (1986). History of the United States of America During the
Adams, Henry. (1910). A Letter to American Teachers of History. Google Books, Scanned PDF. Washington.
Schr?dinger, Erwin (1944). What is Life - the Physical Aspect of the Living Cell. Cambridge University Press. ISBN 0-521-42708-8.
Lovelock, James (1979). GAIA - A New Look at Life on Earth. Oxford University Press. ISBN 0-19-286218-9.
Lehninger, Albert (1993). Principles of Biochemistry, 2nd Ed.. Worth Publishers. ISBN 0-87901-711-2.
Gladyshev, Georgi (1998). Thermodynamic Theory of the Evolution of Living Beings. Nova Science Publishers. ISBN 1560724579.
Gladyshev G. P. (2006). "The Principle of Substance Stability is Applicable to all Levels of Organization of Living Matter" [PDF], Int. J. Mol. Sci., 7, 98-110 - International Journal of Molecular Sciences (IJMS) (ISSN: 1422-0067 Online; ISSN: 1424-6783 CD-ROM; CODEN: IJMCFK).
Avery, John (2003). Information Theory and Evolution. World Scientific. ISBN 981-238-399-9.
http://blog.sciencenet.cn/blog-2444-7728.html 此文来自科学网时东陆博客，转载请注明出处。
上一篇：再论科学的定义
下一篇：关于学刊影响因子的考虑
对于这个问题，如果请文学家和诗人来回答，回答一定是浪漫的。
但是科学家只能依据科学理论来回答这个问题。 他们根据热力学第一和第二定论清楚地阐述了生命的科学定义。生物体与内燃机本来没有区别；前者依赖食物维持生命，后者则需要燃料来发动运行。
物理学的理论和实验结果证明：自然界的过程一般是熵增的过程。但是科学家发现，生命体却是一个熵减的过程。于是生命有了科学的定义：一个熵减的系统。或者说：熵减是生命的特征。
比如，从一般的意义上可以这样来理解：生命体从环境中得到能量(食物与阳光)。这种能量物理上称为自由能。生命体吸收这部分能量而实现细胞的生长与分裂。然后再把吸收的同等能量释放给环境。细胞的生长与分裂是一种从无序到有序列的规则过程 (比如胚胎从不定型长出规则的人体和器官)。这种从比较无序到有序的过程无疑是熵减的。
我们在外星寻找生命时，就可以通过熵减现象来找到生命的蛛丝马迹。
我们一起来看看科学家是如何来定义生命的，很有趣呢！
文章来自： http://en.wikipedia.org/wiki/Entropy_and_life
Entropy and life
In 1910, American historian Henry Adams printed and distributed to university libraries and history professors the small volume A Letter to American Teachers of History proposing a theory of history based on the second law of thermodynamics and the principle of entropy.[1][2] The 1944 book What is Life? by Nobel-laureate physicist Erwin Schroedinger served largely to stimulate this research. In this book, Schroedinger states that life feeds on negative entropy, or negentropy as it is sometimes called. Recent writings have utilized the concept of Gibbs free energy to elaborate on this issue。
Origin
In 1863, Rudolf Clausius published his noted memoir "On the Concentration of Rays of Heat and Light, and on the Limits of its Action" wherein he outlined a preliminary relationship, as based on his own work and that of William Thomson, between his newly developed concept of entropy and life. Building on this, one of the first to speculate on a possible thermodynamic perspective of evolution was the Austrian physicist Ludwig Boltzmann. In 1875, building on the works of Clausius and Kelvin, Boltzmann reasoned:“ The general struggle for existence of animate beings is not a struggle for raw materials – these, for organisms, are air, water and soil, all abundantly available – nor for energy which exists in plenty in any body in the form of heat, but a struggle for entropy, which becomes available through the transition of energy from the hot sun to the cold earth. ”
Early views
In 1876, American civil engineer Richard Sears McCulloch, in his Treatise on the Mechanical Theory of Heat and its Application to the Steam-Engine, which was an early thermodynamics textbook, states, after speaking about the laws of the physical world, that "there are none that are established on a firmer basis than the two general propositions of Joule and Carnot; which constitute the fundamental laws of our subject." McCulloch then goes on to show that these two laws may be combined in a single expression as follows:
S = dQ/τ
where
S = entropy
dQ = equals a differential amount of heat passed into a thermodynamic system
τ = absolute temperature
McCullen then declares that the applications of these two laws, i.e. what are presently known as the first law of thermodynamics and the second law of thermodynamics, are innumerable. He then states:
“ When we reflect how generally physical phenomena are connected with thermal changes and relations, it at once becomes obvious that there are few, if any, branches of natural science which are not more or less dependent upon the great truths under consideration. Nor should it, therefore, be a matter of surprise that already, in the short space of time, not yet one generation, elapsed since the mechanical theory of heat has been freely adopted, whole branches of physical science have been revolutionized by it. ”
McCulloch then gives a few examples of what he calls the “more interesting examples” of the application of these laws in extent and utility. The first example he gives, is physiology wherein he states that “the body of an animal, not less than a steamer, or a locomotive, is truly a heat engine, and the consumption of food in the one is precisely analogous to the burning of fuel in the other; in both, the chemical process is the same: that called combustion.” He then incorporates a discussion of Lavoisier’s theory of respiration with cycles of digestion and excretion, perspiration, but then contradicts Lavoisier with recent findings, such as internal heat generated by friction, according to the new theory of heat, which, according to McCullen, states that the “heat of the body generally and uniformly is diffused instead of being concentrated in the chest”. McCullen then gives an example of the second law, where he states that friction, especially in the smaller blooded-vessels, must develop heat. Without doubt, animal heat is thus in part produced.” He then asks: “but whence the expenditure of energy causing that friction, and which must be itself accounted for?
To answer this question he turns to the mechanical theory of heat and goes on to loosely outline how the heart is what he calls a “force-pump”, which receives blood and sends it to every part of the body, as discovered by William Harvey, that “acts like the piston of an engine and is dependent upon and consequently due to the cycle of nutrition and excretion which sustains physical or organic life.” It is likely, here, that McCulloch was modeling parts of this argument on that of the famous Carnot cycle. In conclusion, he summarizes his first and second law argument as such:“ Everything physical being subject to the law of conservation of energy, it follows that no physiological action can take place except with expenditure of energy derived from food; also, that an animal performing mechanical work must from the same quantity of food generate less heat than one abstaining from exertion, the difference being precisely the heat equivalent of that of work. ”
What is life?
Later, building on this premise, in the famous 1944 book What is Life?, Nobel-laureate physicist Erwin Schroedinger theorizes that life, contrary to the general tendency dictated by the Second law of thermodynamics, decreases or maintains its entropy by feeding on negative entropy.[3] In a note to What is Life?, however, Schr?dinger explains his usage of this term:
“ Let me say first, that if I had been catering for them [physicists] alone I should have let the discussion turn on free energy instead. It is the more familiar notion in this context. But this highly technical term seemed linguistically too near to energy for making the average reader alive to the contrast between the two things. ”
This is what is argued to differentiate life from other forms of matter organization. In this direction, although life's dynamics may be argued to go against the tendency of second law, which states that the entropy of an isolated system tends to increase, it does not in any way conflict or invalidate this law, because the principle that entropy can only increase or remain constant applies only to a closed system which is adiabatically isolated, meaning no heat can enter or leave. Whenever a system can exchange either heat or matter with its environment, an entropy decrease of that system is entirely compatible with the second law.[4] The common justification for this argument, for example, according to renowned chemical engineer Kenneth Denbigh, from his 1955 book The Principles of Chemical Equilibrium, is that "living organisms are open to their environment and can build up at the expense of foodstuffs which they take in and degrade."[4]
In 1964, James Lovelock was among a group of scientists who were requested by NASA to make a theoretical life detection system to look for life on Mars during the upcoming space mission. When thinking about this problem, Lovelock wondered “how can we be sure that Martian life, if any, will reveal itself to tests based on Earth’s lifestyle?” [5] To Lovelock, the basic question was “What is life, and how should it be recognized?” When speaking about this puzzling issue with some of his colleagues at the Jet Propulsion Laboratory, he was asked, well what would you do to look for life on Mars? To this Lovelock replied：“ I’d look for an entropy reduction, since this must be a general characteristic of life. ”
Thus, according to Lovelock, to find signs of life, one must look for a “reduction or a reversal of entropy.”
Gibbs free energy
In recent years, the thermodynamic interpretation of evolution in relation to entropy has begun to utilize the concept of the Gibbs free energy, rather than entropy. This is because biological processes on earth take place at roughly constant temperature and pressure, a situation in which the Gibbs free energy is an especially useful way to express the second law of thermodynamics. The Gibbs free energy is given by:
dG = dH-TdS
The minimization of the Gibbs free energy is a form of the principle of minimum energy, which follows from the entropy maximization principle for closed systems. Moreover, the Gibbs free energy equation, in modified form, can be utilized for open systems when chemical potential terms are included in the energy balance equation. In a popular 1982 textbook Principles of Biochemistry by noted American biochemist Albert Lehninger, it is argued that the order produced within cells as they grow and divide is more than compensated for by the disorder they create in their surroundings in the course of growth and division. In short, according to Lehninger, "living organisms preserve their internal order by taking from their surroundings free energy, in the form of nutrients or sunlight, and returning to their surroundings an equal amount of energy as heat and entropy."[6]
In 1998, noted Russian physical chemist Georgi Gladyshev, in his book Thermodynamic Theory of the Evolution of Living Beings, argues that evolution of living beings is governed by the tendency for quasi-equilibrium, semi-closed, hierarchical living systems to evolve in the direction that tends to minimize the Gibbs free energy of formation of each structure.[7][8] Variations of the Gibbs function of formation of a thermodynamic system at any stage of the evolution, for instance ontogenesis and phylogenesis, such as a social system, according to Gladyshev, "can be calculated by means of thermodynamic methods." Gladyshev calls this a form of sociological thermodynamics.
Similarly, according to the chemist John Avery, from his recent 2003 book Information Theory and Evolution, we find a presentation in which the phenomenon of life, including its origin and evolution, as well as human cultural evolution, has its basis in the background of thermodynamics, statistical mechanics, and information theory. The (apparent) paradox between the second law of thermodynamics and the high degree of order and complexity produced by living systems, according to Avery, has its resolution "in the information content of the Gibbs free energy that enters the biosphere from outside sources."[9]
References
Adams, Henry. (1986). History of the United States of America During the
Adams, Henry. (1910). A Letter to American Teachers of History. Google Books, Scanned PDF. Washington.
Schr?dinger, Erwin (1944). What is Life - the Physical Aspect of the Living Cell. Cambridge University Press. ISBN 0-521-42708-8.
Lovelock, James (1979). GAIA - A New Look at Life on Earth. Oxford University Press. ISBN 0-19-286218-9.
Lehninger, Albert (1993). Principles of Biochemistry, 2nd Ed.. Worth Publishers. ISBN 0-87901-711-2.
Gladyshev, Georgi (1998). Thermodynamic Theory of the Evolution of Living Beings. Nova Science Publishers. ISBN 1560724579.
Gladyshev G. P. (2006). "The Principle of Substance Stability is Applicable to all Levels of Organization of Living Matter" [PDF], Int. J. Mol. Sci., 7, 98-110 - International Journal of Molecular Sciences (IJMS) (ISSN: 1422-0067 Online; ISSN: 1424-6783 CD-ROM; CODEN: IJMCFK).
Avery, John (2003). Information Theory and Evolution. World Scientific. ISBN 981-238-399-9.
http://blog.sciencenet.cn/blog-2444-7728.html 此文来自科学网时东陆博客，转载请注明出处。
上一篇：再论科学的定义
下一篇：关于学刊影响因子的考虑
1 张能立
该博文允许实名用户评论 评论 (8 个评论)
- [8]鲍得海
- 说了半天,只是解释了"生命"的一个物理学表现特征---熵减.
文章根本没讨论"为什么会熵减?"
当人类知道什么是"生命"? "生命力"又是什么? "生命力"从何而来?
---就离上帝不远了!
- [7][游客]修正熵原理
- 70年代，普里高津笼统的熵变公式指出开放系统在外界熵流的输入下，总熵会减小，对应着有序。这种说法竟在广大“群众”中广为流传，因为老百姓似乎都知道，熵是一个无序的度量，有序应该熵减。对开放系统来说，这种简单而笼统的熵变公式及对有序的解释存在严重问题。对开放系统来说，熵原理修正为最大流原理（即约束条件的流或熵最大）更科学。
- [6][游客]songjianguo
- 熵减不是认识生命的一个合理视角。过于片面和简化了。
- [5][游客]动力学的极值特性
- 任意形式的运动都是动力学问题，都可以用微分方程来描述（当然很多时候写不出来或写出来也非常复杂），这些动力学问题都可以转化成变分问题（也即极值问题，历史上哲学家眼中的目的论），当然极值问题随动力学问题不同而多种多样，
哈密顿原理（或最小作用量原理）是其总称。经典的哈密顿原理（或最小作用量原理）面对机械世界的动力学问题，而对像生命这样的开放非线性系统，经典的哈密顿原理（或最小作用量原理）需修正为最大流原理（或开放系统的熵原理），这种极值的存在似乎为当前学术界重新抬头的生命的目的论找到了科学依据。
- [4]吴中祥
- 物质运动有多种形态,
物理学研究的只是最基础的运动形态!
但是,它又是最普遍的运动形态,
它又普遍存在于较高级的运动形态之中!
比物理运动高级的有化学,除有物理的运动形态而外,
还有化学性质变化的运动形态!
其中,从无机化学到有机化学,也是其运动由低级到高级发展的!
而生命就进入到了更高级的运动形态,
其中除与物理\化学的全部运动形态有关而外,
还有可以复制自己\新陈代谢等生物特性的运动形态!
必须注意:
高级运动形态中,都还含有较低级运动形态中所没有的运动特性!
- [3][游客]最大流原理
- 正如薛定锷所言，回答“生命什么的问题”需要新物理学原理，这样的原理必然能描述远离平衡态的开放系统的有序结构，也必须能体现可自我复制。过去几年中，最大流原理作为一个新物理学原理，似乎展现了这方面的潜力。推荐论文：推荐论文：生命是什么:一个基于新物理学原理的回答（见：医学与哲学，2005 Vol.26 No.6 P.16-17,21）
- [2]周旭
- 时兄的文章甚是有趣。熵减固然重要，但是生命信息的可自我复制和自我修复也很重要。否则，所有自组织的物理现象，比如水表面的硬币紧密排列，自然界晶体的规则生长，都是熵减。希望能与兄多交流交流。
- [1][游客]7
- 好文,分析透彻.
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