無止境的認知

林巍

人類對于自然世界2的認識經歷了漫長的過程。希臘哲學家德謨克利特在公元前450年認為，宇宙萬物是由一種細微3而不可分割的物質構成。中國古代哲學家認為，世界是由金、木、水、火、土五種元素組成。到了近現代，又發現了質子、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世紀30年代以前，根據經典物理學，物質是由分子和比分子小的原子構成;分子是物質中能夠獨立存在、相對穩定4、保持其物質化學性質的最小單位。原子是化學反應的基本微粒，在化學反應中不可分割。

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，蘇聯物理學家伊萬年科提出了“質子—中子說”。經科學家研究證實，原子由中心帶正電的原子核與核外高速運轉帶負電的電子構成;原子核由質子和中子兩種粒子構成。1964年，美國物理學家默里·蓋爾曼提出新理論：質子和中子并非是最基本的顆粒，它們由更微小的物質——“夸克”構成。經過幾十年的研究，雖然有的實驗證實了夸克的存在，但單個的夸克至今還未找到。科學家們認為，夸克只能在束縛態內穩定存在，而不能單獨存在，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.

就物理學的理論發展而言，以牛頓力學為基礎的經典物理學，在17世紀提出了“物質不滅”或“實體不變”的理論，將物質視為實體，認為在任何機械運動及化學反應中，質量始終如一。然而，到了20世紀，愛因斯坦的“相對論”指出了物質實體觀的謬誤，認為質量與速度有關，同一物體相對于不同的參考系，其質量就有不同的值。例如，物體運動接近光速時，不斷地對物體施加能量，物體速度的增加卻越來越難，原因何在？其實能量并沒有消失，而是轉化成了質量。再如，原子彈的核裂變和鏈式反應，證明了質量可以變成巨大的能量釋放出來。

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世紀后期，物理學界又出現了“弦理論”，認為自然界物質的基本單元不是電子、光子、中微子或夸克之類的粒子，而是無數微小弦的閉合圈;正是因為它們的不同振動和運動，產生出了各種不同的基本粒子。換言之，無論宏觀世界（星際銀河）或微觀世界（基本粒子），都是由“能量弦”組成的。

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”.

所有這一切，還都是就“能見物質”而言的。然而，據科學家研究，人類對于世界的認知5，目前為止也只有很小一部分。例如，人們所能看到的物質，只有百分之五，而對于構成宇宙的百分之九十五的暗物質，還幾乎一無所知，因為它既不發射也不吸收任何光或電磁輻射，人們只有靠引力效應來推測它的存在。所以，我們對于自然世界的認知，其實才剛剛開始。

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.