譯者：蔡坤憲 出版社：天下文化 出版日期：2019/02/25 大哉問之一：上帝存在嗎？ 科學已開始回答許多原本屬於宗教領域的問題。宗教是人類早期的嘗試，希望能回答我們共有的疑問：我們為何會在這裡？我們從何而來？ 從很久以前開始，答案便幾乎只有一個：神造萬物。這個世界其實是一個相當恐怖的地方，因此即使強悍如維京人，也相信有超自然的神存在，從而去理解一些諸如閃電、暴風雨與月食等自然現象。現在，即使科學已經為這些自然現象提供了更好、也更具一致性的答案，但還是有許多人仍舊依附在宗教上，因為宗教給了他們慰藉，而且他們也不信任或不瞭解科學。 上帝沒有創造宇宙 幾年前，《泰晤士報》的頭版標題是〈霍金說：上帝沒有創造宇宙〉。這篇文章的插畫擷取了米開朗基羅著名畫作《創造亞當》中，生命之火從上帝的右食指傳遞給了亞當的畫面。文章下方，附帶一張我看起來像是沾沾自喜的照片。整個版面看起來，似乎是我與上帝展開決鬥的樣子。然而，我對上帝完全沒有絲毫怨恨。我也不希望給大家一個錯誤的印象，認為我的科學研究工作與「證明上帝是否存在」有關。我的科研工作，是希望尋求一個理性的架構，可以用來理解我們身處的這個宇宙。 數個世紀以來，人們一直相信，像我這樣的身心殘障人士，是受到了來自上帝的詛咒。好吧，也許我真的是得罪了「上面的某人」，但我傾向於認為，每一件發生的事都有另外的一種解釋方式，譬如自然律（law of nature）。假如你像我一樣相信科學，認為自然界中有些定律是牢不可破的。你若喜歡，你也可以說這些定律是上帝的傑作；但這比較接近是「上帝」這個稱謂的定義，而不是證明上帝存在的證據。 大約在西元前三百年，古希臘的哲學家阿里斯塔克斯（Aristarchus）對於各種食（eclipse），特別是月食，感到非常有興趣。他很有勇氣的提問了：是否真的需要由神來引發月食或日食現象？ 阿里斯塔克斯可算是真正的科學先驅。他仔細觀測與研究天象，得出一個大膽的結論：月食是由於地球的影子投射在月球上，而不是一件神蹟。由此發現而解開的思想束縛，讓他可以真正搞清楚，在他的頭頂上方到底發生了什麼事，他並且繪出太陽、地球與月球三者之間，真正的幾何關係。 由此，他得出一個更為驚人的結論：地球不是位於宇宙的中心，而是位在一個繞著太陽運行的軌道上。這與當時所有人的想法都不同。 事實上，他的這份理解，可以完美解釋所有的食：當月球的影子投射到地球上時，發生日食；而當地球的影子投射到月球上時，發生月食。不僅如此，阿里斯塔克斯再進一步推論：天空中的星星，不是當時人們普遍認為的，是天堂地板上的裂縫，而是像我們的太陽一樣，只不過是距離非常遙遠的太陽。 「自然律」就是愛因斯坦和我的上帝 這是一個多麼迷人、多麼讓人讚嘆的領悟啊！這個宇宙就像是一部機器，依循著少數幾條原理或定律在運作，而我們人類的心靈，竟然可以理解這些定律。 我相信，發現這些定律，是人類最偉大的一項成就；這些我們現在稱為「自然律」的東西，將告訴我們，我們是否真的需要一位上帝，來解釋這個宇宙。 這些自然律確切描述了，各項事物在過去、現在與未來的運作方式。例如打網球時，這顆球總會根據這些定律的指示，飛往它該去的地方。掌管世間事物的定律不只這一條，還有許多其他的定律，例如能量如何從網球選手的肌肉，轉換成揮拍的力量；再如草地球場上，這些綠草的生長速率快或慢。然而最重要的是，這些物理定律不僅容不得任何的修改，而且適用於萬事萬物——不僅適用於飛在空中的網球，也適用於行星運動，以及宇宙中的每一樣東西。它們與人類制定的法律不同，對自然律而言，沒有「違法」這回事，這就是它們為何如此有威力、有權威的緣故，這也是為什麼從宗教的角度來看，它們非常具有爭議性。 如果你也像我一樣，可以接受這些自然律是固定的、牢不可破的，那麼很快你就想問：上帝在這裡扮演了什麼角色？這是存在於科學與宗教之間的一個重大矛盾，雖然我在不久之前才登上報紙的頭條新聞，但這卻是一個淵源已久的古老矛盾。我們或許可以定義，上帝是這些自然律的化身。然而，這卻不是大多數人心目中的上帝形象。大家心目中的上帝，是個像人一樣，且可以和我們建立個人關係的神。然而，當你仔細去思索宇宙的浩瀚，以及人類的渺小與偶然時，這種上帝的形象似乎就顯得讓人難以接受了。 跟愛因斯坦一樣，我使用「上帝」這個詞，也是採取一種非人格的態度，指的是自然律。因此，所謂瞭解上帝的心靈，其實就是瞭解這些自然律。我個人的預測是，在二十一世紀末之前，我們便會瞭解上帝的心靈。 宇宙來自空無 目前，創世（宇宙的起源）是宗教還能置喙的領域，然而，即使是這個領域，科學也已經有長足的進展，相信在不久的將來，也能為宇宙的創生，提供明確的答案。我之前出版了一本書，主要討論上帝是否創造了宇宙，結果引起了一些騷動。科學家就宗教議題發表言論，的確讓人惱火。我無意去勸說別人，該去相信什麼，但對我而言，思考上帝是否存在，是一個真真切切的科學問題。畢竟，我們很難再去找到一個比這個問題更重要、更基本、也更神祕的問題：究竟是什麼，或是誰，創造並主宰了這個宇宙？ 根據科學定律，我認為，宇宙是從空無（nothing）之中很突然的、自發誕生出來的。科學的基本假設是「科學決定論」：若已知道系統某個時刻的狀態，那麼科學定律便能決定該系統（宇宙）後續的種種演化過程。這些定律可以是由上帝所頒布的，也可以不是；但無論如何，上帝都無法再干擾或違背這些定律，否則這些就不能稱為定律了。 如此一來，上帝僅剩的自由，便只剩下決定宇宙創生之時的初始狀態了。然而，即使是那個瞬間，也可能有一些必須遵守的定律。換言之，上帝在決定這些事情上面，是根本不享有任何自由的。 宇宙級「食譜」 除去宇宙的複雜與多樣性暫且不論，試想一下，如果我們想創造出一個宇宙，我們需要哪些材料？讓我們像在寫食譜那樣，把這些材料寫下來。對於宇宙「這道菜」，我們需要準備哪些材料呢？ 首先是物質；所有的物體都具有質量。我們的四周充滿了各式各樣的物質，不論是在腳底下、頭頂的天空中，甚或是在太空之中。灰塵、岩石、冰塊、液體等等，都是物質。散布在浩瀚而難以想像的距離之外，那些巨大的氣雲、為數眾多的螺旋星系、以及每個星系之中的那數十億顆恆星，也都是物質。 能量，是我們需要的第二樣材料。即使你從來沒有思考過這個問題，我們也都知道能量是什麼。它是我們每天生活都會遭遇到的東西。抬頭看看太陽，你的臉立刻就能感受到它的熱，這是從一億五千萬公里遠的恆星傳來的能量。能量在宇宙之中穿梭，驅動各式各樣的過程，讓宇宙成為一個生生不息、充滿變化的地方。 現在我們有了物質，也有了能量，第三樣材料則是空間，很大、很大的空間。你可以用很多方式來形容宇宙：令人讚嘆的、美麗的、猛烈的，但是你絕對不能用擁擠、狹小來形容它。無論我們望向何處，總會看到空間，而且愈看，看到的空間愈多、也愈廣闊。 環顧四面八方，所有這些物質、能量與空間，究竟從何而來？我們一直等到二十世紀，才開始有些頭緒。 這個答案，來自於一個人的洞察，他也許是有史以來最了不起的科學家。他就是愛因斯坦。我很遺憾，自己沒有機會和他碰面，因為他過世時，我只有十三歲。 愛因斯坦理解到一件相當特殊的事情：兩樣構成宇宙的主要材料，質量與能量，基本上是同一樣東西，你可以把它想成是一枚銅板的兩面。他最著名的方程式 E = mc2基本上就是說：可以把質量想成是某種形式的能量，反之亦然。所以，現在構成宇宙的材料，不再是三樣，而是只有兩樣：能量與空間。 那麼，所有這些能量與空間，又是從哪裡來的呢？經過數十年的研究，科學家終於找到答案了：空間與能量是在一個我們如今稱為大霹靂的事件中，自發創生出來的。 在大霹靂的那一瞬間，整個宇宙就此出現，並與空間一起存在。它開始暴脹，就像氣球被吹氣膨脹那樣。那麼所有這些能量與空間，究竟來自何處？這個充滿能量、有著浩瀚驚人的空間、以及擁有那麼多萬事萬物的宇宙，如何能從空無之中突然出現？如何無中生有？ 對某些人而言，這就是上帝現身的地方。上帝，就是創造這些能量與空間的造物主；大霹靂，就是創世紀的時刻。然而，科學卻有另外一個版本的故事。冒著讓自己惹上麻煩的風險，我想：我們現在已經可以理解，當初讓維京人感到害怕與恐懼的一些自然現象；我們甚至可以超越愛因斯坦所提出的能量與物質這個優美的對稱關係；我們更可以根據自然律，來探討宇宙的起源，並試著問自己，是否「上帝存在」是宇宙創生的唯一解釋。 第二次世界大戰之後，我在英國長大，那是一個艱困的時期。我們被教導說，天下沒有白吃的午餐、沒有不勞而獲的道理。不過，經過我這一輩子的研究之後，我發現事實上，你可以「免費」獲得一整個宇宙！ 宇宙中必須存在「負能量」 整個大霹靂理論的核心，最難以理解的地方是：如何去解釋這整個宇宙，這一個擁有如此龐大空間與能量的宇宙，是如何從空無之中，被創造出來而成為實體？這個秘密就隱藏在一個奇特而難解的事實裡。根據物理理論的強烈要求，我們這個宇宙中，必須存在一種稱為「負能量」（negative energy）的東西。 為了幫助你理解這個詭異而又關鍵的觀念，讓我以一個簡單的比喻來解釋。想像有人想在平地上，堆起一座山丘，這座山丘代表我們的宇宙。為了要堆出這座山丘，他得在地上挖洞，並用挖出來的土，來堆起這座山丘。然而細想一下，這個人不僅正堆起一座山丘，他同時也挖出了一個坑窪。事實上，這個坑窪，就是山丘的「負版本」。原本在這個坑窪裡的東西，全部都變成了山丘，也就是說山丘與坑莲，二者剛好可以完全抵消、平衡。這就是發生在宇宙創生之初，背後所遵循的原理。 當大霹靂在製造出巨大能量的同時，它也生產出相同大小的負能量。順著這個思維，正負能量相加，結果必然為零。這就是另一個自然律（能量守恆律）。 那麼，這些負能量現在到哪裡去呢？答案是，它就在我們宇宙食譜中的第三樣材料裡：它存在於空間之中。這聽起來可能有點奇怪，不過根據描述重力與運動的這些自然律（也就是古老的牛頓萬有引力定律），空間本身就是一個可以儲藏負能量的巨大容器。它大到足夠把所有的東西都加起來之後，結果為零。 我必須承認，除非你的數學很厲害，不然這個觀念有點難懂，但它卻是千真萬確的。宇宙有上千億個星系，每個星系平均又有數百億顆星球，各自之間，彼此均有重力相吸引；這個綿密的重力之網，就像是一個巨大的能量儲存裝置。宇宙就像是儲藏著負能量的巨大電池。在「正」的東西這邊，是我們今日所能見的質量與能量，也就是那座山丘。而相對應的那個坑窪，也就是在「負」的東西那邊，則遍布在整個宇宙的空間之中。 所以，對於我們希望知道「上帝是否存在」這個問題而言，上述的這些想法有何意義可言？如果說，整個宇宙的總和就是空無一物，那麼其實我們並不需要有一位上帝來創造它。因為，宇宙根本就是一份頂級的免費午餐。 胡桃殼裡的宇宙 由於我們已經知道，正、負相加之後的結果為零，那麼接下來的問題就是：是什麼（或我膽敢問，是誰）在最初的時刻，啟動了這一系列的過程？是什麼讓宇宙可以自發創生？ 乍聽之下，這似乎是一個讓人感到困惑的問題，畢竟在日常生活中，沒有什麼事會自己無端發生。譬如，在你想喝咖啡的時候，你不可能只是單純坐在那裡，敲敲手指頭，就會有一杯咖啡自己泡好並送上來。為了要喝這杯咖啡，你得做很多事，譬如去拿咖啡豆、燒水，也許還需要加上糖牛奶。 但是，當我們想像著縮小自己的身體尺寸，進入咖啡杯裡，再縮小成牛奶分子，再縮小到原子、甚至是次原子的尺度，這時候，你所身處的世界裡，像「無中生有」這種魔術般的奇特現象，並非不可能發生。至少，在短暫的一段時間裡，是可能出現的。這是因為，在這個尺度下，例如質子這類的粒子，它們的行為是由我們稱為量子力學的自然律所規範。它們的確可以隨機出現，彼此聚在一起一陣子，然後又消失不見，隨後又在某處出現。 由於我們知道，宇宙的尺寸會經一度非常微小，也許比質子還小。這意味著一件相當特別的事：這個浩瀚與複雜到令人難以置信的宇宙，可能很簡單就是突然出現，而開始存在，卻完全不需要違反目前已知的自然律。從那一瞬間開始，我們看到，伴隨著巨大的能量被釋放出來的同時，它本身的空間也開始擴張，而在增加出來的空間裡所儲存的負能量，正好可以抵消這些釋放出來的正能量。 當然，這個關鍵問題又再次出現：我們需要上帝來創造量子力學，從而使得大霹靂得以發生嗎？在胡桃殼裡，我們需要一位上帝來做好這些準備，以便大霹靂發生嗎？我無意冒犯任何人的信仰，但是我認為，比起需要一位神聖的造物主，科學所提出的解釋更具有說服力。 時間與空間密不可分 日常的生活經驗，會讓我們認為：某件事的發生，必然是由於先前發生的另一件事所引起的。因此，很自然的一個推理就是：我們需要某個東西（也許是上帝）來創造出這個宇宙。 然而，當我們把宇宙視為一個整體時，情況就變得不太一樣了。讓我稍微解釋一下。想像有一條河，從山上順流而下。這條河的來源、起因是什麼？好吧，可以是因為先前落在山上的雨水所造成的。但是，這些雨水又是哪裡來的呢？太陽，應該是個比較好的答案。由於太陽照到海上，使得海水蒸發，上升到空中變成雲，再落下來成為雨水。那麼，又是什麼原因造成太陽的光和熱呢？當然，我們現在知道這是由於核融合一太陽中的氫在融合成氨的時候，釋放出巨大的能量。 到目前為止，聽起來還算不錯。那麼問題又來了，又是從哪裡來的呢？答案是：大霹靂。於是，問題又回到了原點。不過，這裡有一個非常重要的關鍵：自然律本身就告訴我們，宇宙不僅可以無中生有（就能量的觀點，不需要任何的協助，就能直接蹦出來，就像質子），而且，也可能不需要任何特殊的人或物，來啟動大霹靂的開關。什麼都不需要！ 這個解釋，源自於愛因斯坦的理論：宇宙中的時間與空間是密不可分的交織在一起。在大霹靂的瞬間，有一件非常美好的事情，降臨到了時間身上。時間它本身，就這麼誕生了！ 大霹靂之前，時間根本不存在 要想理解這個讓人難以想像的想法，讓我們從想像一個飄浮在太空中的黑洞開始。一個典型的黑洞，是由一顆具有巨大質量的恆星，因為它本身的重力過大，而引起的崩陷所致。由於它的質量非常巨大，以致光線都法掙脫出它的重力吸引，因而成為一個看起來是黑色的星體。 由於黑洞的重力是如此之大，它不僅能讓光線扭曲，也能讓時間扭曲。當一個時鐘在接近黑洞的時候，時鐘會開始變慢。也就是時間本身會開始變慢。現在，假設時鐘已經進入到黑洞裡面（好吧，假設時鐘可以禁得起這個極端巨大的重力摧殘），時鐘事實上是會停下來的。時鐘之所以會停下來，不是因為它壞掉了，而是因為在黑洞裡面並不存在時間這個東西。而這也恰恰解釋了，宇宙在創生那一瞬間的情況。 在過去的數百年裡，我們對於宇宙的瞭解，已有了驚人的進展。我們目前已知的自然律，不僅能解釋宇宙中的一般情況，也能解釋某些極端的情形，例如宇宙的起源與黑洞等等。時間在宇宙創生之初所扮演的角色，我相信，這是移除我們需要一位偉大造物主的最後一把鑰匙，也是告訴我們宇宙是如何自己創生自己的最後關鍵。 當我們順著時間的軌跡往回走，回到大霹靂的那一瞬間，過程中，宇宙的尺寸會愈來愈小，小到最終變成一個點；整個宇宙變成單一的一個在空間上無限小、密度卻無限大的黑洞，就和目前飄浮在太空中的許多黑洞一樣，也都必須遵守自然律來行事。其中最特別的是，無論是大霹靂那一瞬間的這個黑洞，或是目前飄浮在太空中的眾多黑洞，時間都必須是靜止的。也就是說，你無法得知大霹靂之前的時間為何，因為時間在大霹靂之前根本就不存在。 現在，我們終於發現一個「沒有前因」的東西：由於大霹靂沒有「時間上的之前」，所以它不需要原因就能發生。對我而言，這表示造物主不可能存在，因為在大霹靂之前，「沒有時間」容得下這位造物主。 努力活過此生，影響後世 人們渴望獲得一些大哉問的解答，例如我們為什麼會在這裡？沒有人預期答案會是簡單的，因此，大家也都有要做些努力與奮鬥的準備。當有人問我「上帝是否創造了宇宙？」，我的回答是：這個問題本身沒有意義。在大霹靂之前，時間根本就不存在，因此「沒有時間」讓上帝去創造這個宇宙。 就像有人問「地球的邊界在哪裡？」一樣，由於地球是圓的，所以根本就不存在邊界的問題。因此，若想去尋訪地球的邊界，必定是徒勞無功的努力。 我有信仰嗎？我們每個人都有自由，去相信自己想要相信的。而我的觀點是，最簡單的解釋方式是上帝並不存在。這個宇宙不是由任何人創造的，也沒有任何人可以主宰我們的命運，也許天堂和死後的世界都是不存在的。死後猶存，指的是我們的影響力，以及我們傳給下一代的基因。我們能有此生來欣賞宇宙，對此我深表感恩。 | |
By Stephen Hawking Science is increasingly answering questions that used to be the province of religion. Religion was an early attempt to answer the questions we all ask: why are we here, where did we come from? Long ago, the answer was almost always the same: gods made everything. The world was a scary place, so even people as tough as the Vikings believed in supernatural beings to make sense of natural phenomena like lightning, storms or eclipse. Nowadays, science provides better and more consistent answers, but people will always cling to religion, because it gives comfort, and they do not trust or understand science. A few years ago, The Times newspaper ran a head-line on the front page which said ‘Hawking: God Did Not Create Universe’. The article was illustrated. God was shown in a drawing by Michelangelo, looking thunderous. They printed a photo of me, looking smug. They made it look like a duel between us. But I don’t have a grudge against God. I do not want to give the impression that my work is about proving or disproving the existence of God. My work is about finding a rational framework to understand the universe around us. For centuries, it was believed that disabled people like me were living under a curse that was inflicted by God. Well, I suppose it’s possible that I’ve upset someone up there, but I prefer to think that everything can be explained another way, by the laws of nature. If you believe in science, like I do, you believe that there are certain laws that are always obeyed. If you like, you can say that the laws are the work of God, but that is more a definition of God than a proof of his existence. In about 300 BCE, a philosopher called Aristarchus was fascinated by eclipses, especially eclipses of the Moon. He was brave enough to question whether they really were caused by gods. Aristarchus was a true scientific pioneer. He studied the heavens carefully and reached a bold conclusion: he realized the eclipse was really the shadow of the Earth passing over the Moon, and not a divine event. Liberated by this discovery, he was able to work out what was really going on above his head, and draw diagrams that showed the true relationship of the Sun, the Earth and the Moon. From there he reached even more remarkable conclusions. He deduced that the Earth was not the center of the universe, as everyone had thought, but it instead orbits the Sun. In fact, understand this arrangement explains all eclipses. When the Moon casts its shadow on the Earth, that’s a solar eclipse. And when the Earth shades the Moon, that’s a lunar eclipse. But Aristarchus took it even further. He suggested that stars were not chinks in the floor of heavens, as his contemporaries believed, but that stars are other suns, like ours, only a very long way away. What a stunning realization it must have been. The universe is a machine governed by principles or laws – laws that can be understood by the human mind. I believe that the discovery of these laws has been humankind’s greatest achievements, for its these laws of nature – as we now call them – that will tell us whether we need a god to explain the universe at all. The laws of nature are a description of how things actually work in the past, present and future. In tennis, the ball always goes exactly where they say it will. And there are other laws at work here too. They govern everything that is going on, from how the energy of the shot is produced in the player’s muscle to the speed at which the grass grows beneath their feet. But what’s really important is that these physical laws, as well as being unchangeable, are universal. They apply not just to the flight of a ball, but to the motion of a planet, and everything else in the universe. Unlike laws made by humans, the laws of nature cannot be broken – that’s why they are so powerful and, when seen from a religious standpoint, controversial too. If you accept, as I do, that the laws of nature are fixed, then it doesn’t take long to ask: what role is there for God? This is a big part of the contradiction between science and religion, and although my views have made headline, it is actually an ancient conflict. One could define God as the embodiment of the laws of nature. However, this is not what most people would think of as God. They mean a human-like being, with whom one can have a personal relationship. When you look at the vast size of the universe, and how insignificant and accidental human life is in it, that seems most implausible. I used the word ‘God’ in an impersonal sense, like Einstein did, for the laws of nature, so knowing the mind of God is knowing the laws of nature. My prediction is that we will know the mind of God by the end of this century. The one remaining area that religion can now lay claim to is the origin of the universe. But even here science is making progress and should soon provide a definitive answer to how the universe began. I published a book that asked if God created the universe, and that caused something of a stir. People got upset that a scientist should have anything to say on the matter of religion. I have no desire to tell anyone what to believe, but for me asking if God exists is a valid question for science. After all, it is hard to think of a more important, or fundamental, mystery than what, or who created and controls the universe. I think the universe is spontaneously created out of nothing, according to the law of science. The basic assumption of science is scientific determinism. The laws of science determine the evolution of universe, given its state at one time. These laws may, or may not, have decreed by God, but he cannot intervene to break the laws or they would not be laws. That leaves God with the freedom to choose the initial state of the universe, but even here it seems there may be laws. So God would have no freedom at all. Despite the complexity and variety of the universe, it turns out that to make one you just need three ingredients. Let’s imagine that we could list them in some cosmic cookbook. So what are the three ingredients we need to cook up a universe? The first is matter – stuff that has mass. Matter is all around us, in the ground beneath our feet and out in space. Dust, rock, ice, liquids. Vast clouds of gas, massive spirals of stars, each containing billions of suns, stretching away from incredible distances. The second thing you need is energy. Even if you’ve never thought about it, we all know what energy is. Something we encounter every day. Look up the Sun and you can feel it in your face: energy produced by a star ninety-three million miles away. Energy permeates the universe, driving the process that keep it a dynamic, endlessly changing place. So we have matter and we have energy. The third thing we need to build a universe is space. Lots of space. You can call the universe many things – awesome, beautiful, violent – but one thing you can’t call it is cramped. Wherever we look we see space, more space and even more space. Stretching in all directions. It’s enough to make your head spin. So where could all this matter, energy and space come from? We had no idea until the twentieth century. The answer came from the insights of one man, probably the most remarkable scientist who has ever lived. His name was Albert Einstein. Sadly, I never got to meet him, since I was only thirteen when he died. Einstein realized something quite extraordinary: that two of the main ingredients needed to make the universe – mass and energy – are basically the same thing, two sides of the same coin if you like. His famous equation, E=mc2 simply mean that mass can be thought of as a kind of energy, and vice versa. So instead of three ingredients, we can now say that the universe has just two: energy and space. So where did all this energy and space come from? The answer was found after decades of work by scientists: space and time were spontaneously invented in an event we now called the Big Bang. At the moment of the Big Bang, an entire universe came into existence, and with it, space. It all inflated, just like a balloon being blow up. So where did all this energy and space come from? How does an entire universe full of energy, the awesome vastness of space and everything in it, simply appear out of nothing? For some, this is where God comes back into the picture. It was God who created the energy and space. The Big Bang was the moment of creation. But science tells a different story. At the risk of getting myself into trouble, I think we can understand much more the natural phenomena that terrified the Vikings. We can even go beyond the beautiful symmetry of energy and matter discovered by Einstein. We can use the laws of nature to address the very origins of the universe, and discover if the existence of God is the only way to explain it. As I was growing up in England after the Second World War, it was a time of austerity. We were told that you never get something for nothing. But now, after a lifetime of work, I think that actually you can get a whole universe for free. The great mystery at the heart of the Big Bang is to explain how an entire, fantastically enormous universe of space and energy can materialize out of nothing. The secrete lies in one of the strangest facts about our cosmos. The laws of physics demand the existence of something called ‘negative energy’. To help you get your head around this weird but crucial concept, let me draw on a simply analogy. Imagine a man wants to build a hill on a flat piece of land. The hill will represent the universe. To make this hill he digs a hole in the ground and uses that soil to build his hill. But of course he’s not just making a hill – he’s also making a hole, in effect a negative version of the hill. The stuff that was in the hole has now become the hill, so it all perfectly balances out. This is the principle behind what happened at the beginning of the universe. When the Big Bang produced a massive amount of positive energy, it simultaneously produced same amount of negative energy. In this way, the positive and the negative add up to zero, always. It’s another law of nature. So where is all this negative energy today? It’s in the third ingredient in our cosmic cookbook: it’s in space. This may sound odd, but according to the laws of nature concerning gravity and motion – laws that are among the oldest in science – space itself is a vast store of negative energy. Enough to ensure that everything adds up to zero. I’ll admit that, unless mathematics is your thing, this is hard to grasp, but it’s true. The endless web of billions up billions of galaxies, each pulling on each other by the force of gravity, acts like a giant storage device. The universe is like an enormous battery storing negative energy. The positive side of things – the mass and energy we see today – is like the hill. The corresponding hole, or negative side of things, is spread throughout space. So what does this mean in our quest to find out if there is a God? It means that if the universe adds up to nothing, then you don’t need a God to create it. The universe is the ultimate free lunch. Since we know that the positive and the negative add up to zero, all we need to do now is to work out what – or dare I say who – triggered the whole process in the first place. What could cause the spontaneous appearance of a universe? At first, it seems a baffling problem – after all, in our daily lives thing don’t just materialize out of the blue. You can’t just click your fingers and summon up a cup of coffee when you feel like one. You have to make it out of other stuff like coffee bean, water and perhaps some milk and sugar. But travel down to this coffee cup – through the milk particles, down to the atomic level and right down to the sub-atomic level, and you enter a world where conjuring something out of nothing is possible. At least, for a short while. That’s because, at this scale, particles such as protons behave according to the law of nature we call quantum mechanics. And they really can appear at random, stick around for a while and then vanish again, to reappear somewhere else. Since we know that the positive and the negative add up to zero, all we need to do now is to work out what – or dare I say who – triggered the whole process in the first place. What could cause the spontaneous appearance of a universe? At first, it seems a baffling problem – after all, in our daily lives thing don’t just materialize out of the blue. You can’t just click your fingers and summon up a cup of coffee when you feel like one. You have to make it out of other stuff like coffee bean, water and perhaps some milk and sugar. But travel down to this coffee cup – through the milk particles, down to the atomic level and right down to the sub-atomic level, and you enter a world where conjuring something out of nothing is possible. At least, for a short while. That’s because, at this scale, particles such as protons behave according to the law of nature we call quantum mechanics. And they really can appear at random, stick around for a while and then vanish again, to reappear somewhere else. Since we know the universe itself was once very small – perhaps smaller than a proton – this means something quite remarkable. It means the universe itself, in all its mind-boggling vastness and complexity, could simply have popped into existence without violating the known laws of nature. From that moment on, vast amounts of energy were released as space itself expanded – a place to store all the negative energy needed to balance the book. But of course the critical question is raised again: did God created the quantum laws that allowed the Big Bang to occur? In a nutshell, do we need a God to set it up so that the Big Bang could bang? I have no desire to offend anyone of faith, but I think science has a more compelling explanation than a divine creator. Our everyday experience makes us think that everything that happens must be caused by something that occurred earlier in time, so it’s natural for us to think that something - maybe God – must have caused the universe to come into existence. But when we’re talking about the universe as a whole, that isn’t necessarily so. Let me explain. Imagine a river, flowing down a mountainside. What caused the river? Well, perhaps the rain that fell earlier in the mountains. But then, what caused the rain? A good answer would be the Sun, that shone down on the ocean and lifted water vapor up into the sky and made clouds. Okay, so what caused the Sun to shine? Well, if we look inside we see the process known as fusion, in which hydrogen atoms join to form helium, releasing vast quantities of energy in the process. So far so good. Where does the hydrogen come from? Answer: the Big Bang. But here’s the crucial bit. The laws of nature itself tell us that not only could the universe have popped into existence without any assistance, like a proton, and have required nothing in terms of energy, but also that it is possible that nothing caused the Big Bang. Nothing. The explanation lies back with the theories of Einstein, and his insights into how space and time in the universe are fundamentally intertwined. Something very wonderful happened to time at the instant of the Big Bang. Time itself began. To understand this mind-boggling idea, consider a black hole floating in space. A typical black hole is a star so massive that it has collapsed in on itself. It’s so massive that not even light can escape its gravity, which is why it’s almost perfectly black. It’s gravitational pull is so powerful, it warps and distorts not only light but also time. To see how, imagine a clock is being sucked into it. As the clock gets closer and closer to the black hole, it begins to get slower and slower. Time itself begins to slow down. Now imagine the clock as it enters the black hole – well, assuming of course that it could withstand the extreme gravitational forces – it would actually stop. It stops not because it is broken, but because inside the black hole time itself doesn’t exist. And that’s exactly what happened at the start of the universe. In the last hundred years, we have made spectacular advances in our understanding of the universe. We now know the laws that govern what happens in all but the most extreme conditions, like the origin of the universe, or black holes. The role played by time at the beginning of the universe is, I believe, the final key to removing the need for a grand designer and revealing how the universe created itself. As we travel back in time towards the moment of the Big Bang, the universe gets smaller and smaller and smaller, until it finally comes to a point where the whole universe is a space so small that it is in effect a single infinitesimally small, infinitely dense black hole, floating around in space, the laws of nature dictates something quite extraordinary. They tell us hat here too time itself must come to a stop. You can’t get to a time before the Big Bang because there was no time before the Big Bang. We have finally found something that doesn’t have a cause, because there was no time to a cause to exist in. For me this means that there is no possibility of a creator, because there is no time for a creator to have existed in. People want answer to big questions, like why we are here. They don’t expect the answer to be easy, so they are prepared to struggle a bit. When people ask me if a God created the universe, I tell them that the question itself makes no sense. Time didn’t exist before the Big Bang so there is no time for God to make the universe in. It’s like asking for directions to the edge of the Earth – the Earth is a sphere that doesn’t have an edge, so looking for it is a futile exercise. Do I have faith? We are each free to believe what we want, and it’s my view that the simplest explanation is that there is no God. No one created the universe and no one directs our fate. This leads me to a profound realization: there is probably no heaven and afterlife either. I think believe in an afterlife is just wishful thinking. There is no reliable evidence for it, and it flies in the face of everything we know in science. I think that when we die we return to dust. But there’s a sense in which we live on, in our influence, and in our genes that we pass on to our children. We have this one life to appreciate the grand design of the universe, and for that I am extremely grateful. From Brief Answers to the Big Questions by Stephen Hawking， John Murray Publishers (2018) | |
咁簡單嘅問題，一下就解決，有啥好拗呢? |