2010年05月11日08:20
來源：《科技日報》
據英國《每日電訊報》5月10日（北京時間）報道，為驗証愛因斯坦廣義相對論中關於引力波的預言是否正確，美歐航天部門將合作研制3個航天器，這些航天器發射后將繞太陽公轉，在相距300萬千米的距離上相互發射激光束，以在茫茫宇宙中搜尋低頻引力波的“倩影”。
這是美國宇航局與歐洲航天局的一項“大手筆”合作。他們正在共同研發的航天器將在太空中同一軌道運行，航天器之間的激光束被點火后，將可測量出懸浮在每個探測器上的金—鉑金立方體之間相對位置的變化。科學家認為，這些相對位置的變化或由微弱的引力波引起。這一試圖直接觀測到引力波的“麗莎”（LISA，太空激光干涉天線）計劃被認為是有史以來最偉大的舉動。
引力波也稱重力波。早在1916年，愛因斯坦提出廣義相對論時就預言了引力波的存在。他認為，諸如星系或黑洞等大的物體相互碰撞會導致空間出現波紋，這種波紋就叫做引力波。引力波由於攜帶能量，應可被探測到。但由於引力波的強度很弱，物質對其吸收效率也極低，使得直接探測引力波極為困難。
國際研究團隊負責人、英國格拉斯哥大學引力波專家金·霍夫表示，引力波是愛因斯坦廣義相對論中最后一個需要証明正確與否的謎題，但迄今為止，科學家還隻能搜尋到高頻率的引力波。而“麗莎”計劃可利用激光干涉方法精確測量信號相位，傾聽黑洞相遇時的“喃喃低語”，探測來自宇宙間遙遠的引力波源的微弱低頻引力波。
“麗莎”項目最終完成的時間將在2020年左右。其先行測試計劃中的“麗莎探路者”（LISA Pathfinder）預計於明年發射，將為探測引力波鋪平道路。“麗莎探路者”的制造商表示，要測量諸如恆星系統崩塌或是巨大黑洞碰撞等宇宙事件，需要超高精度的技術，測量的位置變化將精確到40萬億分之一米。
科學家希望，一旦探測到引力波，他們將依據所獲取的獨一無二的寶貴材料來繪制大爆炸發生后一瞬間的宇宙“肖像”。
格拉斯哥大學的引力波專家希拉·羅萬稱，來自於黑洞周圍彎曲時空中的引力波將給人們提供看待引力波或是了解崩坍恆星內物質狀態的新視角，同時也將讓人們更好地了解電磁輻射、光以及黑洞和恆星的成因。（劉霞）
又是一項催生諾貝爾獎得主的偉大科學工程。10年后讓諾獎評委們面紅耳赤的，或許不是頒不頒的分歧，而是頒幾個的爭執。在愛因斯坦看來，萬有引力的本質是波動。就像電荷加速時產生電磁波一樣，質量加速時發出引力波，這是廣義相對論的著名預言。其實，引力波的存在早被間接証實，缺的只是第一手憑據。如果進展順利，直接探測引力波作為實驗物理學中最重要的課題之一，其在給老愛蓋棺定論的同時，也必將為人類開啟一扇眺望宇宙的全新窗口。
http://scitech.people.com.cn/BIG5/11561583.html
有史以來最大的科學儀器去證明愛因斯坦的廣義相對論理論
Largest scientific instrument ever built to prove Einstein's theory of general relativity
Three spacecraft flying three million miles apart are to fire laser beams at each other across the emptiness of space in a bid to finally prove whether a theory proposed by Albert Einstein is correct.
3架太空船分開飛行三百萬哩，向彼此間發射激光束穿越空洞的太空，企圖最終證明愛因斯坦提出的理論是否正確的。
By Richard Gray, Science Correspondent
Published: 8:30AM BST 09 May 2010
Albert Einstein was awarded the Nobel Prize for Physics in 1921 Photo: AFP/GETTY愛因斯坦在1921年獲得諾貝爾物理學獎 照片：法新社/蓋蒂
Physicists hope the ambitious mission will allow them to prove the existence of gravitational waves – a phenomenon predicted in Einstein's famous theory of general relativity and the last piece of his theory still to be proved correct.
物理學家們希望雄心勃勃的任務，將讓他們去證明引力波的存在 - 一種現象由愛因斯坦著名的理論廣義相對論所預言，和他的理論的最後一塊仍有待證明是正確的。
The mission, a collaboration between Nasa and the European Space Agency, will use three spacecraft flying in formation while orbiting the sun, with each housing floating cubes of gold platinum.
此次任務是由美國宇航局和歐洲航天局之間合作，將使用三部太空船列隊飛行，同時繞過太陽，每一部的外罩浮起金鉑立方體。
Laser beams fired between the spacecraft will then be used to measure minute changes in the distance between each of the cubes, caused by the weak waves of gravity that ripple out from catastrophic events in deep space.
在太空船之間發射的激光束，隨後將被用來量度在每個立方體之間的距離的精密變化，由微弱的引力波所造成，那從深空中的災難性事件輕蕩出。
Einstein's theory of general relativity predicted that when large objects such as black holes collide, ripples in space and time flow outwards. These ripples are called gravitational waves.
愛因斯坦的廣義相對論的理論預測，當大的物體例如黑洞碰撞，在太空起漣漪和時間向外流動，這些漣漪被稱為引力波。
A panel of international experts have now set out a detailed plan for the mission and how it can be used to reveal new insights about the universe around us.
一隊國際專家小組已為任務訂出詳細的計劃，和它如何被用以揭示有關環繞我們的宇宙的新見解。
Professor Jim Hough, an expert on gravitational waves at Glasgow University and a member of the committee that drew up the plans, said: "Gravitational waves are the last piece of Einstein's theory of general relativity that has still to be proved correct.
"They are produced when massive objects like black holes or collapsed stars accelerate through space, perhaps because they being pulled towards another object with greater gravitational pull like a massive black hole.
"Unfortunately we haven't been able to detect them yet because they are very weak. However, the new experiments we are working on have great potential to allow detection."
Ground based attempts to detect gravitational waves on Earth have so far been unsuccessful and can only look for gravitational waves with relatively high frequencies.
Scientists have already been able to prove a number of predictions made by Einstein's theory of general relativity, including that light is bent by gravity, gravity travels at a constant speed, that time can be warped by gravity and that space and time can bend.
Einstein's other theories including his most famous formula E=mc2 have also withstood scientific testing.
The Laser Interferometer Space Antenna, or LISA as the new space based mission is called, will be able to detect gravitational waves of very low frequencies due to the huge distance between the three spacecraft. It will be the largest detector ever built.
A smaller test mission called LISA Pathfinder, which is being built by British engineers at space company Astrium EADS and is due to be launched next year, is to pave the way for the more ambitious mission by demonstrating the technology to be used to detect the waves.
Scientists have already begun building the instruments that will be used in LISA itself, but it is not expected to be launched before 2020.
They hope that once detected, gravitational waves will be able to provide new information about the universe that cannot currently be seen using electromagnetic radiation such as light, radio waves and X-rays.
Professor Sheila Rowan, who also studies gravitational waves at Glasgow University, added: "Black holes are so dense that no light or radiation escapes from inside them.
"Gravitational waves from the warped spacetime around black holes could give us new ways of looking at them.
"We could also learn about the state of matter inside collapsed stars."
Dr Ralph Cordey, science and exploration business development manager at Astrium UK who are building LISA Pathfinder, said: "Trying to measure cosmic events such as collapsing star systems or the collision of massive black holes throughout our universe requires ultra-high precision technology.
"The ultimate goal is to prove that this technology works, before we attempt to put three spacecraft into orbits at a distance of 5 million kilometres from one another, connected only by a laser beam that will measure their positions accurate to 40 millionths of a millionth of a metre."
http://www.telegraph.co.uk/science/space/7695994/Largest-scientific-instrument-ever-built-to-prove-Einsteins-theory-of-general-relativity.html
世界上最強大的激光 今年引發聚變反應
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