无止境的认知

林巍

人类对于自然世界2的认识经历了漫长的过程。希腊哲学家德谟克利特在公元前450年认为，宇宙万物是由一种细微3而不可分割的物质构成。中国古代哲学家认为，世界是由金、木、水、火、土五种元素组成。到了近现代，又发现了质子、中子、夸克。

Human understanding of the physical world has gone through a lengthy development process. In 450 BC， the Greek philosopher Democritus believed that everything in the universe was made up of a tiny and indivisible substance. Philosophers in ancient China thought that the world was composed of five elements： gold， wood， water， fire， and earth. In modern times， protons， neutrons and quarks have subsequently been found.

在20世纪30年代以前，根据经典物理学，物质是由分子和比分子小的原子构成;分子是物质中能够独立存在、相对稳定4、保持其物质化学性质的最小单位。原子是化学反应的基本微粒，在化学反应中不可分割。

By the 1930s， according to classical physics， matter is composed of molecules and atoms which are smaller than molecules. Molecules are the smallest units of matter in terms of existence， stability and chemical properties; atoms are the basic indivisible particles in chemical reactions.

1932年，蘇联物理学家伊万年科提出了“质子—中子说”。经科学家研究证实，原子由中心带正电的原子核与核外高速运转带负电的电子构成;原子核由质子和中子两种粒子构成。1964年，美国物理学家默里·盖尔曼提出新理论：质子和中子并非是最基本的颗粒，它们由更微小的物质——“夸克”构成。经过几十年的研究，虽然有的实验证实了夸克的存在，但单个的夸克至今还未找到。科学家们认为，夸克只能在束缚态内稳定存在，而不能单独存在，且瞬息即逝。

But in 1932， the Soviet physicist Dimitri Ivanenko proposed his “proton-neutron theory”. Scientists proved that an atom consists of a positively charged nucleus （made up of protons and neutrons） and negatively charged electrons revolving around it at high speed. In 1964， American physicist Murray Gell-Mann put forward a new theory， which held that protons and neutrons are not the smallest particles， since they are made up of quarks. After several decades of research， although the existence of quarks has been confirmed by experiments， no single quark has so far yet been isolated. Scientists thus believe that quarks are fleeting and exist only under certain stable and confining conditions.

就物理学的理论发展而言，以牛顿力学为基础的经典物理学，在17世纪提出了“物质不灭”或“实体不变”的理论，将物质视为实体，认为在任何机械运动及化学反应中，质量始终如一。然而，到了20世纪，爱因斯坦的“相对论”指出了物质实体观的谬误，认为质量与速度有关，同一物体相对于不同的参考系，其质量就有不同的值。例如，物体运动接近光速时，不断地对物体施加能量，物体速度的增加却越来越难，原因何在？其实能量并没有消失，而是转化成了质量。再如，原子弹的核裂变和链式反应，证明了质量可以变成巨大的能量释放出来。

On the theoretical front， in the 17th century classical physics， based on Newtonian mechanics， put forward the theory of the “conservation of matter” or “entity invariance”， regarding matter as an entity which remains constant under any mechanical movement and chemical reaction. However， in the 20th century， Einstein pointed out the fallacy of this theory in his Relativity， relating mass to speed since the quality of the same matter varies with different reference systems. For example， when an object moves close to the speed of light， it is increasingly hard to speed up despite more energy being infused. Why is that？ The energy， rather than disappearing， is instead transformed into mass. Also， it has been proved that mass can be transformed into immense energy through nuclear fission in the chain reaction of an atomic bomb.

到了20世纪后期，物理学界又出现了“弦理论”，认为自然界物质的基本单元不是电子、光子、中微子或夸克之类的粒子，而是无数微小弦的闭合圈;正是因为它们的不同振动和运动，产生出了各种不同的基本粒子。换言之，无论宏观世界（星际银河）或微观世界（基本粒子），都是由“能量弦”组成的。

By the late 20th century， “string theory” had emerged in the field of physics， believing that the basic units in the physical world are not particles such as electrons， photons， neutrinos， or quarks， but numerous tiny closed loop strings， whose vibrations and movements produce various basic particles. In other words， both the macroscopic world （e.g. the Milky Way galaxy） and microscopic world （e.g. fundamental particles） are made up of “energy strings”.

所有这一切，还都是就“能见物质”而言的。然而，据科学家研究，人类对于世界的认知5，目前为止也只有很小一部分。例如，人们所能看到的物质，只有百分之五，而对于构成宇宙的百分之九十五的暗物质，还几乎一无所知，因为它既不发射也不吸收任何光或电磁辐射，人们只有靠引力效应来推测它的存在。所以，我們对于自然世界的认知，其实才刚刚开始。

All this is about “visible matter”. According to scientific research， however， the knowledge humanity has so far acquired covers only a tiny part of the universe. Visible matter detectable by humans， for example， accounts for just 5%， the rest （dark matter） making up 95% of the cosmos， which， neither emitting nor absorbing any light or other electromagnetic radiation at any significant level and inferred only from its gravitational effects on visible matter， still remains almost unknown to humans. Therefore， our journey to identify and understand the physical world has in fact only just begun.