Toppling the Giant

推倒巨人

By Graham P. Collins

作者╱柯林斯 ( Graham P. Collins )
譯者╱郭兆林

　　Everyone wants to get a piece of Einstein. Two of the three most common crackpot missives received by scientists and science magazines involve Einstein: claims to have a unified theory (succeeding where Einstein failed) and claims to have proved his theories false. (The third big class of craziness: perpetual-motion machines and infinite-energy sources.) Like cannibals seeking the strength and life spirit of their victims, these misguided amateurs seem to think that by outdoing or disproving Einstein they will acquire all his prestige and acclaim. Of course, all that they disprove is their own competence with basic relativity.

　　每個人都想和愛因斯坦沾上邊。科學家與科學雜誌最常接到的三種唬人研究，有兩種與愛因斯坦有關：宣稱發現統一理論（想在愛因斯坦失敗之處成功）及證明愛因斯坦的理論錯誤。（至於第三大類狂人，會提到永動機及無窮盡的能源。）就像食人族企圖奪取受害者的精神氣力般，這些誤入歧途的業餘人士似乎認為，只要超越愛因斯坦或證明愛因斯坦的錯誤，便可以接收他所有的聲名權威。當然，他們只不過證明自己對基本相對論的無知罷了。

　　But the crazies are not the only iconoclasts. Many serious and well-qualified researchers also seek to go beyond Einstein, in the way that he went beyond Galileo and Newton. The accompanying article by Alan Kostelecký describes the experimental search for departures from Einsteinian relativity. The analysis he discusses is based on a general “Standard Model Extension” in which all plausible relativity-violating terms are added to the equations of particle physics. This all-encompassing model covers every possible deviation that could trickle down to everyday physics from the high-energy pinnacle of the (as yet undiscovered) ultimate unified theory.

　　但挑戰權威者並非只有狂人。有許多認真且夠資格的研究者也企圖超越愛因斯坦，就像愛因斯坦超越伽利略與牛頓一般。寇斯托利基這篇文章，便是談到悖離愛氏相對論的實驗研究。他的討論大致上以「標準模型延伸」為分析依據，這個理論將所有看似可能的相對論違逆項，加入粒子物理學的方程式中。這個包山包海的模型涵括所有可能的悖離情況，從終極統一理論（雖尚未發現）的頂峰滲透到日常生活的物理學中。

　　Yet certain putative breaches of relativity have attracted specific attention. One class of theories goes by the name “doubly special relativity,” which has been studied by Giovanni Amelino-Camelia of the University of Rome since 2000 and later by Lee Smolin of the Perimeter Institute for Theoretical Physics in Ontario, João Magueijo of Imperial College London and others. Magueijo, incidentally, fits the label “iconoclast” to a T—as is apparent from his argumentative book Faster Than the Speed of Light.

　　不過，某些猜想的相對論違逆已經引起相當的注意力。其中有一派理論稱為「雙重狹義相對論」，由義大利羅馬大學的阿梅利諾–卡梅力亞（Giovanni Amelino-Camelia）自2000年開始研究，後來是加拿大安大略省圓周理論物理研究院的斯莫林（Lee Smolin），以及英國倫敦帝國學院的馬古悠（João Magueijo）等。其中，馬古悠更是符合「挑戰權威者」的標籤，這點從他那本爭議性的著作《比光速還快》可明顯看出。

　　Doubly special relativity is inspired by quantum gravity theories such as loop quantum gravity [see “Atoms of Space and Time,” by Lee Smolin; SCIENTIFIC AMERICAN, January], and it imposes a second kind of “speed limit” that works in conjunction with the conventional barrier of the speed of light in a vacuum, also known as c. The idea is that at very short distances the smooth continuity of spacetime should break down into something more granular—like grains of sand or the network of a spider's web. In quantum physics, short distances and short times correspond to high momenta and high energies. Thus, at sufficiently high energy—the so-called Planck energy—a particle should “see” the graininess of spacetime. That violates relativity, which depends on spacetime being smooth down to the tiniest size scales. Reflecting this, in a doubly special theory, just as a particle cannot be accelerated beyond c, it cannot be boosted beyond the Planck energy.

　　雙重狹義相對論受到量子重力理論所啟發，如環圈量子重力理論（參見2004年2月號〈時空原子〉）。此理論設下第二道「速限」，與傳統的以真空光速（c）為限制並行。其想法是在極小的距離之下，時空平順的連續性將會被破壞而成為顆粒狀，看似沙粒或蜘蛛網的網絡。在量子物理學中，短距離與短暫的時間對應的是高動量與高能量，因此在足夠高的能量（即普朗克能量）之下，粒子應該會「看見」時空的顆粒狀，也就會出現相對論違逆，因為相對論假設時空一直到極微小的尺度規模仍是平順的。為了反映這一點，在雙重狹義理論中粒子不僅不能加速到超越c，也不能推進到超越普朗克能量。

　　Some of these models predict that extremely high frequency light should travel faster than lower-frequency light. Experimenters are looking for that effect in light from distant explosions called gamma-ray bursts.

　　其中有些模型預測極高頻的光會走得比低頻光更快，實驗者正在尋找遠方γ射線爆發的光線裡是否具此效應。

　　But skeptics are unconvinced that these theories are well founded. Some researchers argue, for example, that the equations are physically equivalent to ordinary relativity, just dressed up in enough complexities for that to be unobvious. The proof of the pudding will have to come from a rigorous derivation of such a theory from something more fundamental, such as string theory or loop quantum gravity. Not to mention experimental evidence.

　　但是懷疑者不相信這些理論站得住腳。例如，有些研究者主張這些方程式在物理學上與平常的相對論完全相同，只是以複雜的外衣加以包裝，使大家不容易看出來。最後的定奪必須從更基本的理論嚴謹推導而出，例如弦論或環圈量子重力，而需要實驗證據就更不用說了。

　　Another infraction that some have contemplated is that c itself has varied over the history of the universe. John W. Moffat of the University of Toronto studied models of this type in the early 1990s, and Magueijo has been a more recent champion of them. If c had been much greater in the very early moments of the big bang, certain effects could have propagated at an extremely fast rate, which would solve some cosmological puzzles.

　　另外，有些人想像中的相對論違逆理論，真空光速c本身會隨宇宙演進而發生改變，加拿大多倫多大學的莫菲特（John W. Moffat）於1990年代早期開始研究這類模型，馬古悠是此理論最新近的擁護者。若c在大霹靂初期比現在快得多，則某些物理效應可能會以極快的速度傳播，有些宇宙學難題將得以解決。

　　If c varies, so, too, does the fine structure constant, alpha, which is a dimensionless number that specifies the strength of the electromagnetic interaction. Alpha can be expressed in terms of c, Planck's constant and the charge of the electron. Alpha can therefore also change with c remaining constant, which might not infringe on relativity but would be equally seismic. Such variation in alpha could occur in string theory, where the magnitude of alpha depends on the precise structure of extra tiny dimensions that are appended to the four dimensions of space and time that we know and love [see “The String Theory Landscape,” by Raphael Bousso and Joseph Polchinski, on page 78].

　　若c改變，則精細結構常數α也會發生改變；α是不具因次的數字，可決定電磁作用的強度。α可用c、普朗克常數與電子電荷表示，因此當c維持固定時，α也可以改變；雖然這動不了相對論，卻也同具震撼效果。α的違逆可能發生在弦論裡，其中的強度正是由額外的微小維度（除了我們熟悉且喜愛的四維時空之外）的結構所決定（參見第66頁〈一統宇宙的弦論〉）。

　　The possibility that alpha might change was considered as long ago as 1955, by the great Russian physicist Lev Landau. Today physicists and astronomers are looking at ancient light from distant quasars for evidence that alpha was slightly different eons ago. Changing alpha would subtly alter the frequency of light emitted or absorbed by atoms and ions. Most searches for such shifts have turned up empty thus far.

　　α可能發生改變的想法，早在1955年時偉大的蘇俄物理學家蘭道（Lev Landau）便思索過。今日的物理學家與天文學家正試圖從遠方類星體傳來的古老光線，尋找漫長歲月前α曾經改變過的證據。改變的α將會微妙的改變原子、離子所吸收或放射出的光線頻率，不過至今絕大多數搜尋這種變化的努力都落得一場空。

　　One exception is the results of a group led by John K. Webb of the University of New South Wales in Australia. Those researchers have used a novel method of analyzing the data to achieve finer precision and have reported evidence (albeit statistically somewhat weak) of shifts: between eight billion and 11 billion years ago, alpha appears to have been about six parts in a million feebler than it is today. Such a minute variation is hard to reconcile with the string theory explanation, which predicts long-term stability of constants such as alpha, punctuated by occasional catastrophic changes of great magnitude.

　　其中有一個例外，是澳洲新南威爾斯大學的韋布（John K. Webb）所領導的研究團隊。這些研究人員利用一種新穎的資料分析法提高精確度，並且已經提出α變化的證據（雖然在統計上略顯薄弱）：在80億到110億年前，α比現代值小百萬分之六。這個渺小的變化值很難與弦論的解釋相容，因為弦論預測如α等常數是長期穩定，然後突然劇烈大幅改變其值。

　　Some researchers, however, assert that the precision claimed by the new method is not correct and that the “shifts” are just statistical fluctuations. In March of this year a team of astronomers led by Patrick Petitjean of the Institute of Astrophysics of Paris and the Observatory of Paris and Raghunathan Srianand of the Inter-University Center for Astronomy and Astrophysics in Pune, India, reported using the traditional methods pushed to the limit. They concluded that as far back as 10 billion years, alpha has changed by less than 0.6 part in a million, contradicting the claims of Webb and company.

　　不過有些研究者認為，這種新方法所宣稱的精準並不正確，而其所謂的「變化」不過只是統計上的起伏而已。今年3月由巴黎天文物理研究所與巴黎天文台的佩提特金（Patrick Petitjean）與印度普納的大學校際物理暨天文物理中心的席恩（Raghunathan Srianand）所帶領的天文學家，將傳統的方法推至極限，結果發現在百億年前，α值改變不到千萬分之六，與韋布等人所宣稱的有段差距。

　　So far then, Einstein has withstood all challengers. The iconoclasts will have to keep looking for the first chink in his armor.

　　所以到目前為止，愛因斯坦還是抗退群倫。想要挑戰權威的人士，勢必得繼續尋找愛因斯坦的罩門了。