海遠繼續在本文略為介紹《The God Particle:If the Universe Is the Answer, What Is the Question?》(以下簡稱《The God Particle》)〈Chapter 7: A-tom!〉,這本書第七章內容涵括基礎粒子。

「A-tom」(原子) 本意是「not divisible」(不能分割);但二十世紀的科研顯示,「原子」其實是由更基本的粒子所構成,也就是網誌327一文所說的「the fundamental particles of the Standard Model」。

「標準模型」(Standard Model) 是一項理論。本質上,這個模型假設無法再加以分割的物質粒子有兩種,分別是「夸克」(quark) 和「輕子」(leptons)。不同種類的夸克構成了「質子」(proton) 和「中子」(neutron);最常見的輕子則是「電子」(electron)。適當比例的夸克和輕子可構成各種原子,再進一步構成宇宙中的各種物質。

這些構成物質的粒子由「四種力」結合在一起,分別是大眾相當熟悉的「重力」(gravity) 和「電磁力」(electromagnetism),及較不熟悉的「強核力」(strong nuclear force) 和「弱核力」(weak nuclear force)。電磁力與強、弱核力是透過交換「玻色子」來傳遞。海遠引述下列有關標準模型的一些資料:

「standard model of the atom」–
According to this model, matter can be divided into the following building blocks: Quarks, Leptons and Bosons.

(1) quarks – elementary particles that do participate in holding the nucleus together. Quarks are extremely small particles (less than 10-15 m radius) that participate in the strong nuclear force. Isolated (single) quarks have never been found, probably because they combine with each other so quickly. Quarks also have fractional electric charges. They are classified as follows:

•down (d) – charge = -1/3
•up (u) – charge = +2/3
•strange (s) – charge = -1/3
•charm (c) – charge = +2/3
•bottom (b) – charge = -1/3
•top (t) – charge = +2/3 (most massive, discovered in 1995)

As of now, quarks are thought to be the most fundamental particles.

(2) leptons – elementary particles that do not participate in holding the nucleus together (examples – electron, neutrino) . Leptons are extremely small particles (less than 10-15 m radius) that have no known size or internal structure. They have tiny masses, travel very fast and are best described by wave functions. The best known examples of leptons are the electron and the neutrino.

(3) There are four known types of forces –
(a) Strong – holds the nucleus of the atom together
(b) Weak – involved in radioactive decay
(c) Electromagnetism – interactions between charged particles (electricity and magnetism)
(d) Gravity – attractive force based on mass and distance

Bosons – particles that carry forces. There are four known bosons:

•Gluon – mediates the strong force, but only operates over distances of 10-13 cm (10 to the power minus thirteen)

•W and Z – mediate the weak force (1/10,000 strong force), but only operate over distances of 10-15 cm (10 to the power minus fifteen)

•Photon – mediates electromagnetic force (1/137 strong force) and operates over an infinite distance

A fifth gauge particle (graviton) has been proposed, but has not yet been found. The graviton is thought to mediate gravity, which is 10-39 strong force and operates over an infinite distance.

The Standard Model of elementary particles, with the three generations of matter (in columns), gauge bosons in the fourth column and the Higgs boson in the fifth. Atoms are composed of 「protons」and「neutrons」, and each is a combination of three「first generation quarks」:

•Proton = 2 「up quarks」 + 1「 down quark」;proton has +1 charge = (+2/3) + (+2/3) + (-1/3).

•Neutron = 2 「down quarks」+ 1 「up quark」;neutron has 0 charge = (-1/3) + (-1/3) + (+2/3).
Electron belongs to 「first generation leptons」.

從附圖一及二所顯示,標準模型中的粒子有六種是夸克(以紫色表示),有六種是輕子(以綠色表示),在這兩類粒子右邊有四種規範玻色子(以紅色表示),最右邊是希格斯玻色子(以黄色表示)。

我們日常的「物質」是「第一代」(first generation matter),「第二代」和「第三代」物質只存在於高能物理學實驗中。

「第一代」物質由「原子」(atom) 構成,而「原子」由「質子」、「中子」和「電子」構成。質子和中子都是由「第一代夸克」構成;電子則屬「第一代輕子」。

讀者可從互聯網找更多資料 :

“http://upload.wikimedia.org/wikipedia/commons/0/00/Standard_Model_of_Elementary_Particles.svg”;

Standard Model – wiki
“http://en.wikipedia.org/wiki/Standard_Model”;

Elementary particle – wiki
“http://en.wikipedia.org/wiki/Elementary_particle”;

Quark –wiki
“http://en.wikipedia.org/wiki/Quark”;
夸克 維基百科
“http://zh.wikipedia.org/wiki/%E5%A4%B8%E5%85%8B”;

Lepton – wiki
“http://en.wikipedia.org/wiki/Lepton”;
輕子 – 維基百科
http://zh.wikipedia.org/zh-tw/%E8%BC%95%E5%AD%90;

Boson – wiki
“http://en.wikipedia.org/wiki/Boson”;

Gauge boson-wiki
“http://en.wikipedia.org/wiki/Gauge_boson”;

玻色子( baidu)
“http://baike.baidu.com/view/2676.htm”;

Fundamental interaction – wiki
“http://en.wikipedia.org/wiki/Four_forces”;

Timeline of the Standard Model of Physics
“http://rationaldiscoveryblog.com/post/26935967831/timeline-of-the-standard-model-of-physics”;
“http://www.pinterest.com/pin/95068242104701499/”。

「標準模型」的發展歷史(見附圖三):

Timeline of particle discoveries – wiki
“http://en.wikipedia.org/wiki/Timeline_of_particle_discoveries”;

Timeline of particle physics – wiki
“http://en.wikipedia.org/wiki/Timeline_of_particle_physics”;

Timeline of Particle Physics
“http://www.davidterr.com/science-articles/particle_physics.html”;

Modern View (Standard Model) timeline: 1964 – present
“http://www.particleadventure.org/other/history/smt.html”;
“http://pdg.web.cern.ch/pdg/cpep/history/smt.html”;

回顧歷史:
1800–1900:atomic model 建立;
1900–1950:subatomic particles發現:質子、中子、電子;
1950–1975:standard model of elementary particles建立。

夸克和輕子才是不可分割的粒子。2012年,「歐洲核子研究組織」(CERN) 的「大型強子對撞機」(Large Hadron Collider) 發現希格斯玻色子,標準模型理論通過了最後的考驗,但標準模型理論有一最大缺點,就是未能包括「萬有引力」,亦未能包括天文學新發現的「暗物質」、「暗能量」。

1975以後,有物理學家提出「Physics beyond Standard Model」,包括:

「大統一理論」(Grand Unification Theory);
「統一場論」(Unified field theory);
「萬有理論」(Theory of Everything);
「M – Theory」;
「弦理論」( string theory)、「超弦理論」(super string theory) …等。

但這些理論,卻要等待日後做出比大型強子對撞機更强力的粒子對撞實驗,才能測試。

備註:本文部份資料,取材自《The God Particle:If the Universe Is the Answer, What Is the Question?》一書及《維基網頁》,謹此鳴謝。

附圖一:標準模型

atom01

附圖二:標準模型

atom02

附圖三:「標準模型」的發展歷史

atom03

這篇文章發表 於 星期一, 三月 10th, 2014 7:02 下午 在 邁向現代 Road to Modernity. 你可以回應這篇文章透過 RSS 2.0 feed. 你可以 留下回覆, 或 引用 從你的個人網站.

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