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Archive for May, 2007

Quantum theory and the Nobel prize

Tuesday, May 22nd, 2007

Personal prejudices and a lack of understanding by the Nobel-prize committee left the pioneers of quantum mechanics unrewarded until the discovery of antimatter in 1932.

In 1933 the Nobel prizes seemed of little importance compared with the global economic depression and the rise to power of the Nazis, but many physicists still kept a watchful eye on Stockholm. Their bewilderment and chagrin over the most recent decisions by the Royal Swedish Academy of Sciences had fuelled anticipation. No prize had been awarded in physics since 1930, yet recent theoretical and experimental achievements had led to a revolutionary new quantum-mechanical depiction of the atom. Would the Academy finally acknowledge these accomplishments?

When the Academy eventually announced its decision in November, the results pleased some, angered others and puzzled many. The prize reserved from 1932 went to Werner Heisenberg alone for “the creation of quantum mechanics, the application of which has, inter alia, led to the discovery of allotropic forms of hydrogen”. Meanwhile, the 1933 prize was shared by Erwin Schrödinger and Paul Dirac for “the discovery of new productive forms of atomic theory”.

The prizes for quantum mechanics have long been the subject of speculation and gossip. Why were these men the only ones to be rewarded, why were the prizes divided so awkwardly, and why was the official rationale for the awards so odd? More generally, the 1933 decisions point to the broader question that peppers both popular and scholarly histories of modern physics: why were so few Nobel prizes awarded for theoretical contributions? Was this the result of Alfred Nobel’s testament, which specifies that the prize is awarded for “discovery or invention in the field of physics”? Is it inherently more difficult to define a theoretical breakthrough as a discovery?

I have studied the Nobel archives, and the correspondence of former committee members, in an effort to clarify the reasons for the traditional neglect of theory, as well as to make sense of the 1933 prizes. These activities have provided an insight into the committee’s treatment of theoretical accomplishments prior to 1933, which helps us to understand the significance of the awards that year, including the last-minute inclusion of Paul Dirac among the winners.

Academy rewards

The Nobel prizes may well be international in scope but from the start the Royal Swedish Academy of Sciences based its decisions on the recommendations of the five members of the Nobel committees for physics and chemistry. The Swedish committee members’ own judgement, their understanding of science and their interests have been critical to the outcome. Those scientists invited to submit nominations rarely provided the committees with a clear consensus. And even when a single strong candidate did emerge - such as Albert Einstein for relativity theory or Henri Poincaré for various contributions to mathematical physics - the committees often ignored the mandate. A simple change in the composition of the committee could, on occasion, decide the fate of a candidate.

Although the five committee members evaluated the candidates and proposed who should receive a prize, their recommendation still had to be approved by the ten members of the Academy’s Physics Section, and then by the 100 members of the full Academy. Usually the committee’s authority prevailed, but not always. Sometimes the Academy of Sciences rebelled against its committees. In the cases of Gustaf Dalén (1912) and Jean Perrin (1926), members of the Academy successfully rallied their colleagues to overturn the committee’s declaration that these candidates did not merit prizes.

Although formal statutes govern all aspects of the Nobel system, they by no means provide unambiguous guidelines for the committees to go about their business. Such crucial phrases as “most significant discovery or invention in the field of physics” or “recent” or “benefit on mankind” are not defined. Interpretive traditions have arisen and changed over time. But even when everyone involved has tried to rise above pettiness and partiality, the task of selecting winners has always been - and remains - exceedingly difficult. Occasionally committee members have confessed privately that, at times, there have been several equally deserving candidates.

摘自http://physicsweb.org/articles/world/15/8/7,这篇文章较长,只需翻译以上部分。

Gravity Probe B backs general relativity

Monday, May 14th, 2007

A preliminary analysis of data from the Gravity Probe B satellite has confirmed that the Earth’s mass distorts the fabric of space and time as predicted by Einstein’s theory of general relativity. Although this “geodetic effect” has already been proven with greater accuracy through other measurements, the Gravity Probe team claim that their successful analysis paves the way for using data from the satellite to make a very accurate measurement of a second, much subtler consequence of general relativity called “frame-dragging”. However, some physicists are questioning this claim and asking if the final results will be worth the probe’s $700 million price tag.

The Gravity Probe B (GP-B) satellite is a collaboration between NASA and Stanford University and was launched in 2004 with an aim to study two effects predicted by general relativity, a theory first put forth by Einstein in 1915. In addition to the geodetic effect, the theory also predicts that massive bodies will pull space and time along with them as they rotate — an effect called frame dragging.

Now analysis of the data from GP-B has confirmed the geodetic effect with an accuracy of better than one percent. Although the same effect has already been measured by NASA’s Cassini mission, the results indicate that the much subtler frame-dragging effect should be confirmed by further data analysis by the end of this year. Frame-dragging has also been measured before by NASA’s LAGEOS satellites with an accuracy of ten percent, and it is currently unclear whether GP-B data will yield a more accurate result.

Gravity Probe B used superconducting quantum interference devices (SQUIDs) to measure tiny changes in the orientations of four perfectly-spherical, quartz gyroscopes as the experiment orbited the Earth for one year. The gyroscopes were housed inside a vacuum chamber and were maintained at 1.8 Kelvin during the measurements using liquid helium. The probe also includes a telescope that was trained on a distant “guide star” to provide a reference direction for measurements on the gyroscopes. General relativity predicts that the frame-dragging effect will cause the direction of the gyroscopes to change by a tiny 0.041 of an arc second.

Prior to launch, however, the satellite suffered numerous delays, and now there is the possibility that the accuracy of its data will not surpass that of other experiments performed before now. “On one level one can say that [Gravity Probe B] is a fantastic triumph of engineering — nobody has ever done an experiment like this before,” Clive Speake, a physicist from the University of Birmingham, told Physics Web. “On the other hand, one can’t do these experiments for fun. We have to wait until the frame-dragging result comes out.”

原文:Gravity Probe B backs general relativity

参考翻译:

引力探测器B验证广义相对论

对引力探测器B卫星(Gravity Probe B)发送回来数据进行的初步分析表明:地球本身的质量造成了时空结构的扭曲,这和爱因斯坦的广义相对论所预测的一致。在短程线效应(geodetic effect)已经由其它高精度测量手段确认存在后,该项目小组声称对另一广义相对论的预测——坐标系拖曳效应(frame-dragging),也将因此次探测计划的成功而可以进行精确的测量。但仍有学者对此存有疑问,那么最终的实验结果和探测仪器的7亿美元身价是否相称呢?

引力探测器B卫星(GP-B)是美国宇航局和斯坦福大学合作的产物,于2004年发射,其目的就是研究1915年爱因斯坦广义相对论预言的两种效应。除了短程线效应以外,另一个就是坐标系拖曳效应,其表现就是大质量物体会在旋转的同时拖着周围的时空一起旋转。

现在从GP-B所得数据做出的分析可以使短程线效应的测量精度控制在1%以下。虽然美国宇航局的卡西尼计划已经对此进行过测量,此次的结果表明更难探测到的坐标系拖曳效应还需要进行分析,这个工作要持续到年底。之前LAGEOS卫星对坐标系拖曳效应的测量精度为10%,不知道GP-B能获得何种精度的结果。

引力探测器B采用超导量子干涉仪(SQUID)对其搭载在卫星上的四个完美球面石英陀螺仪在一年绕地运行过程中所发生的微小变动进行测量。陀螺仪被安置在真空室内,由液氦处理使温度保持在1.8K。探测器还安装一台望远镜,将其一直对准一颗远距离的“基准恒星”作为测量参照方向。广义相对论预测坐标系拖曳效应会使这些陀螺仪的指向(自转轴)发生0.041弧秒的偏转。

虽然这次发射是优先进行的,不过该项目的实施已经多次延后。现在看起来,测量数据的精确性可能不会超过此前的实验。伯明翰大学的物理学家Clive Speake在接受物理网(Physics Web)采访时表示:“一方面,‘重力探测器B’是一项工程技术领域的梦幻之作,之前从来没有人会想到还可以做这样的实验。不过另一方面,实验不是游戏,我们还需要等待坐标系拖曳效应的最终结果。”

NASA’s royal visit

Tuesday, May 8th, 2007

On Tuesday morning, Queen Elizabeth II is making a visit to NASA’s Goddard Space Flight Center in Greenbelt, Maryland, US. She will visit Goddard’s mission control centre and chat with the crew of the International Space Station, while her husband, the Duke of Edinburgh, will tour facilities used to build and test satellites.

The US and UK have recently moved towards closer ties in space exploration. In April, NASA signed an agreement with the British National Space Centre to study possible collaboration between the two countries for exploration of the Moon and beyond.

The queen does not seem to have a special interest in space and astronomy, but there was an ill-fated Canadian telescope named after her in the 1960s. The Queen Elizabeth II telescope was to be located in the mountains of British Columbia, with a main mirror 4 metres across, which would have made it the second largest in the world at the time.

Sadly, after the mirror was cast, budget cuts forced the cancellation of the project. The mirror was sold off and apparently melted down so the glass could be recycled.

As cool as it might be to visit Goddard, it’s too bad the queen won’t be visiting Cape Canaveral to watch a space launch. I think that would be even more fun. In fact, given her penchant for more adventurous activities like horseback riding, maybe she would even be up for a vacation in space. You never know until you ask.

By David Shiga(原文:NASA’s royal visit

参考译文:

英国女王参观戈达德中心

周二早上(5月8日),英国伊利莎白二世女王将要参观美国航空航天局(NASA)位于马里兰州Greenbelt的戈达德飞行中心(Goddard Space Flight Center)。她将参观戈达德的任务控制中心,并且与国际空间站的机组人员交谈,同时她的丈夫,爱丁堡伯爵也将会参观那些用于建造和检测卫星的设备。

美国和英国近来在空间探索方面的合作越来越密切。四月,NASA与英国国家空间中心(British National Space Centre)签署了一项关于两国在月球探索方面的合作。

女皇看起来在空间和天文上没有特别的兴趣,但是在十九世纪六十年代有一个以她名字命名的倒霉的加拿大望远镜。这个伊利莎白二世女王望远镜位于不列颠哥伦比亚(British Columbia)山上,有直径四米的大镜子,这是当时世界上第二大的。

不幸的是,在这个镜面做好后,经费的削减使得这项工程又被取消了。这个镜子被卖掉后熔化了,以便其中的玻璃可以再循环利用。

尽管女王将参观戈达德,但不会到卡纳维拉尔角(Cape Canaveral)去参观航天飞机发射。我认为那可能会更有趣。事实上,如果她喜欢象骑马之类的冒险运动的话,她甚至可能会想进行一次空间旅行。不过这个除非你亲自去问,否则很难猜到结果。

另一版本的翻译:

NASA迎来王家贵宾

周二早,英女王伊丽莎白二世来到位于美国马里兰州绿带市的戈达德空间飞行中心进行参观。她计划参观这里的控制中心并和国际空间站上的工作人员进行通话。同时她的丈夫爱丁堡公爵将前往参观制造和测试卫星的各种设备。

美英两国逐渐在空间开发领域走在了一起。4月美国宇航局和英国国家空间中心签署了一项协议,讨论在探索月球以及未来一些项目上的合作可能。

女王陛下对空间和天文学并没有特别的喜好,不过在二十世纪六十年代曾有一架加拿大望远镜以女王的名字命名。这架不幸的“伊丽莎白二世”望远镜本来设计安放在不列颠哥伦比亚省的山上,其主镜直径有4米,这台望远镜因此将成为当时世界第二大的望远镜。

遗憾的是,在镜面抛光工作完成后,项目因为预算的削减而被迫下马。主镜也被变卖熔掉回收。

很可惜女王陛下没有去卡纳维拉尔角(的肯尼迪航天中心)观看一次飞船发射的盛况,这可是和空间飞行中心一样能让人感到激动的地方。我觉得去航天中心更有意思一些。实际上,根据女王陛下喜爱骑马这样冒险刺激的运动可以推测,她甚至可能会想去太空游玩。不过不问你是不会知道的。