無(wú)止境的認(rèn)知

林巍

人類對(duì)于自然世界2的認(rèn)識(shí)經(jīng)歷了漫長(zhǎng)的過(guò)程。希臘哲學(xué)家德謨克利特在公元前450年認(rèn)為，宇宙萬(wàn)物是由一種細(xì)微3而不可分割的物質(zhì)構(gòu)成。中國(guó)古代哲學(xué)家認(rèn)為，世界是由金、木、水、火、土五種元素組成。到了近現(xiàn)代，又發(fā)現(xiàn)了質(zhì)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(jì)30年代以前，根據(jù)經(jīng)典物理學(xué)，物質(zhì)是由分子和比分子小的原子構(gòu)成;分子是物質(zhì)中能夠獨(dú)立存在、相對(duì)穩(wěn)定4、保持其物質(zhì)化學(xué)性質(zhì)的最小單位。原子是化學(xué)反應(yīng)的基本微粒，在化學(xué)反應(yīng)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(lián)物理學(xué)家伊萬(wàn)年科提出了“質(zhì)子—中子說(shuō)”。經(jīng)科學(xué)家研究證實(shí)，原子由中心帶正電的原子核與核外高速運(yùn)轉(zhuǎn)帶負(fù)電的電子構(gòu)成;原子核由質(zhì)子和中子兩種粒子構(gòu)成。1964年，美國(guó)物理學(xué)家默里·蓋爾曼提出新理論：質(zhì)子和中子并非是最基本的顆粒，它們由更微小的物質(zhì)——“夸克”構(gòu)成。經(jīng)過(guò)幾十年的研究，雖然有的實(shí)驗(yàn)證實(shí)了夸克的存在，但單個(gè)的夸克至今還未找到?？茖W(xué)家們認(rèn)為，夸克只能在束縛態(tài)內(nèi)穩(wěn)定存在，而不能單獨(dú)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(xué)的理論發(fā)展而言，以牛頓力學(xué)為基礎(chǔ)的經(jīng)典物理學(xué)，在17世紀(jì)提出了“物質(zhì)不滅”或“實(shí)體不變”的理論，將物質(zhì)視為實(shí)體，認(rèn)為在任何機(jī)械運(yùn)動(dòng)及化學(xué)反應(yīng)中，質(zhì)量始終如一。然而，到了20世紀(jì)，愛(ài)因斯坦的“相對(duì)論”指出了物質(zhì)實(shí)體觀的謬誤，認(rèn)為質(zhì)量與速度有關(guān)，同一物體相對(duì)于不同的參考系，其質(zhì)量就有不同的值。例如，物體運(yùn)動(dòng)接近光速時(shí)，不斷地對(duì)物體施加能量，物體速度的增加卻越來(lái)越難，原因何在？其實(shí)能量并沒(méi)有消失，而是轉(zhuǎn)化成了質(zhì)量。再如，原子彈的核裂變和鏈?zhǔn)椒磻?yīng)，證明了質(zhì)量可以變成巨大的能量釋放出來(lái)。

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(jì)后期，物理學(xué)界又出現(xiàn)了“弦理論”，認(rèn)為自然界物質(zhì)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(wú)數(shù)微小弦的閉合圈;正是因?yàn)樗鼈兊牟煌駝?dòng)和運(yùn)動(dòng)，產(chǎn)生出了各種不同的基本粒子。換言之，無(wú)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(jiàn)物質(zhì)”而言的。然而，據(jù)科學(xué)家研究，人類對(duì)于世界的認(rèn)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(zhì)，只有百分之五，而對(duì)于構(gòu)成宇宙的百分之九十五的暗物質(zhì)，還幾乎一無(wú)所知，因?yàn)樗炔话l(fā)射也不吸收任何光或電磁輻射，人們只有靠引力效應(yīng)來(lái)推測(cè)它的存在。所以，我們對(duì)于自然世界的認(rèn)知，其實(shí)才剛剛開(kāi)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.