橙橙小狐狸
Particle physics: The race to break the standard modelThe Large Hadron Collider is the latest attempt to move fundamental physics past the frustratingly successful 'standard model'. But it is not the only way to do it. Geoff Brumfiel surveys the contenders attempting to capture the prize before the collider gets up to speed.Geoff Brumfiel ILLUSTRATIONS BY J. RIORDANIt is powerful; it is galling; it is doomed. The incredibly successful mathematical machine that physicists call the 'standard model' is a set of equations that describes every known form of matter, from individual atoms to the farthest galaxies. It describes three of the four fundamental forces in nature: the strong, weak and electromagnetic interactions. It predicts the outcome of one experiment after another with unprecedented accuracy. And yet, as powerful as it is, the standard model is far from perfect. Its mathematical structure is arbitrary. It is littered with numerical constants that seem equally ad hoc. And perhaps most disturbingly, it has resisted every attempt to incorporate the last fundamental force: gravity.So physicists have been trying to get beyond the standard model ever since it was put together in the 1970s. In effect, they will have to shatter the model with experimental data that contradict its near-perfect equations. And then, from its fragments, they must build a newer, better theory. The Large Hadron Collider (LHC), a giant particle accelerator at CERN, Europe's particle-physics laboratory near Geneva, Switzerland, is the latest attempt to break the standard model — and one that many see as all but assured of success. The prodigious energy it generates will force particles into realms where the standard model cannot follow. In the race to move beyond the status quo, "the LHC is by far the favourite", says Frank Wilczek, a theorist at the Massachusetts Institute of Technology in Cambridge who won the 2004 Nobel Prize in Physics for his work underpinning the standard model.But the LHC is not the only game in town. For decades physicists have tried to get beyond the standard model in all sorts of ways, sometimes with accelerators, sometimes with precision measurements of breathtakingly rare events, sometimes with observation of outer space. And in the time it takes for the LHC to get fully up to speed — its first results aren't expected until at least next summer (see 'The unstoppable collider') — some of those experimental groups think that they have a fighting chance of seizing the prize first. Their task will be hard: the standard model is a formidable piece of work that has resisted all the easy and obvious attacks. To crack it, experiments will need unprecedented sensitivity, a multitude of data, and more than a little luck. Here's a rundown of the heroic few who feel up to the task. TevatronWhile the LHC gets its protons up to speed, the world's other heavyweight particle-accelerator is racing to break the standard model first. Since 2001, the Tevatron, located at Fermilab in Batavia, Illinois, has been accelerating protons and antiprotons at an energy of around 1 tera electron volt.That's only a seventh of the eventual top energy of the LHC, but total energy isn't everything in the hunt for new physics. Collisions that would generate new particles outside the standard model are extremely rare, which means that the longer an accelerator runs and the more data it accumulates, the better its chances of finding something. So for a while, at least, the Tevatron will continue to have a data lead over the LHC. Even by the summer of 2009, the Tevatron will have several times more total data than its new competitor.And already those data are showing some tantalizing, if tentative, hints of something beyond the standard model. One deviation comes in measurements of a particle known as the strange B (Bs) meson. The Bs is made of a strange quark and an anti-bottom quark, and it is among the heaviest of all mesons. Under a rule known as charge-parity symmetry, the standard model predicts the Bs will decay in the same way as its antiparticle (made of an anti-strange and a bottom quark). But measurements of the two are hinting at a difference in their decays. According to Dmitri Denisov, a spokesperson for the D-Zero experiment at the Tevatron, that difference could be an important clue in the quest for discoveries. It might signal the existence of new, exotic particles, or of previously unknown principles. In any case, says Denisov, "it's an exciting measurement".The Bs anomaly is not the only oddity showing up at the accelerator, adds Robert Roser, a spokesperson for the Tevatron's other major experiment, the Collision Detector at Fermilab, or CDF. An unusual feature in the decays of pairs of top and anti-top quarks has him intrigued. Again, he admits, it's far from certain. But some of these signals may turn out to be important, Roser says. "As you add data, one of [these anomalies] may become real."Perhaps not surprisingly, a more sceptical view comes from John Ellis, a theorist at CERN. Yes, the Tevatron could provide some tantalizing hints, says Ellis, but it is unlikely to make a definitive find before the LHC comes on strong. In the world of particle physics, he points out, nothing constitutes a discovery until it is measured to five σ (five standard deviations from the mean), the equivalent of 99.99994267% accuracy. Much more data than the Tevatron has accumulated so far will be needed to reach that exacting standard, and the detector is unlikely to make those big gains before it is overtaken by its new rival. "I think its going to be very, very tough for the Tevatron," Ellis says. "I just don't see them getting it before the LHC starts going gangbusters." CosmosWhile the high-energy physicists gather in their machine's control rooms, another group of physicists is looking to the heavens. There they hope to find something that shatters the standard model — if the Universe cooperates.The main thing that their spacecraft will look for are indications of dark matter, the ghostly substance that could make up as much as 85% of the matter in the Universe. Astronomers know that dark matter exists only because of its gravitational pull on galaxies and its influence on the Universe's shape; it seems to pass right through the kind of ordinary matter found in stars, planets and people. Presumably, dark matter is a haze of particles that rarely, if ever, react with the ordinary variety. But nobody is quite sure what those particles might be — except that they are not accounted for in the standard model.One candidate comes from the 'supersymmetry' theory, which predicts that every particle in the standard model has another, heavier partner lying outside the model. The lightest of these supersymmetric partners is called the neutralino, and is predicted to have just the right properties to be dark matter.Neutralinos themselves wouldn't be seen by telescopes, orbiting or otherwise. But periodically, two neutralinos could collide and annihilate — creating a shower of more mundane particles that orbiting detectors might pick up. The PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) experiment has already seen an intriguing clue. The satellite-borne instrument has unofficially reported a surplus of anti-electrons that may have been generated by dark-matter annihilations (see Nature 454, 808; 2008). "It's a beautiful result," says Graciela Gelmini, a physicist at the University of California, Los Angeles, who has seen PAMELA's data. Still, she adds, the complexities of the measurement require caution.A second, recently launched satellite may also be able to spot the untimely demise of the neutralino. The Fermi Gamma-ray Space Telescope is a US$690-million space instrument designed to scan the entire sky for ultra-high-energy photons. It is possible that such γ-rays could be created by neutralino collisions, in which case they would show up as a ubiquitous haze in the orbiting detector's sky-map. "That would be a stunning, stunning signature," says Steven Ritz, the telescope's project scientist at NASA's Goddard Space Flight Centre in Greenbelt, Maryland.Such signatures, if they're spotted and confirmed in time, definitely have a chance to beat the LHC in the quest to break the standard model, says Michael Turner, a cosmologist at the University of Chicago in Illinois. But Ritz points out that although astrophysics could technically be the first to make such a discovery, they can't do much more than that. Anti-electrons, γ-rays and other such signatures could provide physicists with only a rough mass range for the new particles, and would say nothing about how supersymmetry might work. For those reasons "there would still be a large number of essential question marks", says Ritz — questions that would have to be resolved at the LHC. The darkOther physicists have chosen darkness over light. From their lairs inside disused mines and traffic tunnels, they are watching a number of highly sensitive detectors that could find direct signatures of dark matter, including supersymmetric neutralinos (see Nature 448, 240; 2007).There are around half-a-dozen different schemes for such detectors, but they all follow the same basic concept. Take some stuff you think could respond to dark matter, place it deep underground to protect it from cosmic rays and other disruptive influences, and wait for something to happen. "It's like watching grass grow," says Wilczek.Although they are perhaps not the most exciting way to beat the LHC, these detectors are making impressive progress. One experiment, the Cryogenic Dark Matter Search II, or CDMS II, is currently accumulating data in the Soudan Mine deep beneath Minnesota. Its operators aim to treble its current sensitivity by the end of the year. Another experiment called XENON100, located in a tunnel under Italy's Gran Sasso Mountain, stands a chance to have its first results out before the LHC's detectors can finish processing their findings. "The field is going so fast and there's so much competition, that it's not easy to survive at the moment," says Elena Aprile, the principal investigator for XENON100 at Columbia University in New York. "It's an amazing time."And on top of these prospects, one group claims that it has already seen dark matter in its detector. Earlier this year, the DAMA/LIBRA (Dark Matter Large Sodium Iodide Bulk for Rare Processes) experiment, also at the Gran Sasso National Laboratory, announced that it had seen a signal in its latest generation of detector (see Nature 452, 918; 2008). But their finding has the other groups stumped, says Aprile, whose experiment sits in a vault next to that of DAMA/LIBRA. No one else has yet been able to confirm the signal, and in fact, the findings from other teams seem contradictory, she says. "We are definitely not consistent."Although these detectors seem to be improving in leaps and bounds, they have an Achilles heel: they only work if the so-far unseen dark-matter particles interact, at least occasionally, with regular matter. There's no guarantee that that is the case, says Ellis. And as far as he's concerned, that makes these experiments "shots in the dark".Still, Ellis concedes that there is a chance that these esoteric searches might manage to see something before the LHC can. "I think the dark-matter guys are the jokers in the pack," he says. NeutrinoThe next few months will be a caffeine-fuelled blur for most of those scientists racing to beat the LHC. But neutrino physicists can take it easy: they've already broken new ground, and they did it a decade ago.Neutrinos are the neutral members of the 'lepton' family of particles, the group that includes the electron. The original version of the standard model predicted that neutrinos should be completely massless, but experimentalists suspected otherwise. For years they saw fewer neutrinos from the Sun than theorists predicted. One possible explanation for the deficit was that solar neutrinos could be switching from one type to another. But that switching would be possible only if neutrinos had mass. In 1998, a Japanese experiment in Hida called Super-Kamiokande saw the neutrino switch in action, and that result is the first — and to date the only — firm finding that defies the standard model.Unfortunately, says Ellis, the neutrino's mass can be accommodated within the standard model by making just a few simple modifications to the equations. "It's possible to add something in relatively easily," he says. And consequently, although neutrino physicists can arguably claim the prize, their discovery hasn't helped theorists in their search for new models of physics.But neutrinos may not be finished just yet. Experiments in the United States, Europe and Japan are now firing beams of neutrinos at their detectors to try to learn more about how the neutrinos switch from one kind to another. The precise details of this switching may help narrow the field of possible new theoretical models, says Lisa Randall, a theorist at Harvard University in Cambridge, Massachusetts.And two new detectors could go further still. A European collaboration is now running the Astronomy with a Neutrino Telescope and Abyss Environmental Research (ANTARES) detector under the Mediterranean Sea off the coast of Toulon, France, and a team of Americans is installing IceCube beneath the ice of Antarctica. Both use strings of detectors to see high-energy neutrinos from cosmic sources striking water or ice. ANTARES was completed earlier this summer, whereas IceCube has about half of its 70 strings of detectors installed. But already IceCube is five times more sensitive than Super-Kamiokande, according to Francis Halzen, IceCube's principal investigator at the University of Wisconsin, Madison. "It's not inconceivable we'll find something," he says.Just what that something might be is up for debate. One possibility would be neutrinos produced by dark-matter particles trapped in the Sun's core. But again, Halzen says, anything seen by the neutrino experiments would almost certainly require follow-up by the LHC. "I think these experiments are complementary," he says. "But if you give me a choice, I'd rather see it first." Success?So can any of these projects best the standard model? Wilczek is sceptical. "I'm not on the edge of my seat," he says. Looking the track record, it seems that, "the standard model always wins". He believes that only the LHC stands a real chance of breaking the existing paradigm.ADVERTISEMENTAnd there's no guarantee that even the giant collider will find something new. "Super symmetry could show up anytime between mid-2009 and never," says Ellis. If never is the date, he says, physicists will face "the maximum conceivable horror scenario". "What will we do next?" he asks.But Turner takes a different view. Ultimately, these experiments and the LHC are fighting the battle together. He is confident that by combining their data with the LHC's, the standard model can be bested, and that new physics will be discovered. "We're on the verge of a major revolution," he says.
小蝴蝶飞不过
南极洲是世界上纬度最高，平均海拔最高的大洲。它极寒，干燥，狂风肆虐，即便是安静的极夜也掩盖不了它狂野的内心。这是一个神秘的大洲，而人类从未停止过对这片遥远大陆的 探索 。随着科学的发展，我们的技术逐渐成熟，人类在南极洲建立起了大大小小七十余个科考站。下面我们来看看南极洲那些科考站之最和它们的简介。 阿蒙森·斯科特站是由美国建立的一个科考站，它建立于1957年，位于南极点上，是南极洲纬度最高的的科考站。 阿蒙森·斯科特站以两位探险家命名，他们是来自挪威的罗尔德·阿蒙森和来自英国的罗伯特·斯科特。阿蒙森和斯科特二人竞争最先抵达南极点，最后阿蒙森胜过了斯科特，成为了第一个到达南极点的人。 阿蒙森·斯科特站每年有长达6个月的极夜，这也使它成为了南极洲极夜最长的科考站。由于远离人烟，阿蒙森·斯科特站有着全世界最干净的空气。漫长的极夜，远离电磁干扰与洁净的夜空让阿蒙森·斯科特站成为了观测宇宙最理想的地方。在这里有一个世界最大的中微子天文台——冰立方（IceCube）。 阿蒙森·斯科特在建立之初确实位于南极点上，但是，经过了数十年冰川的运动，现在的阿蒙森·斯科特站已经偏离当初的位置，但它仍然是南极所有科考站当中纬度最高。 昆仑站是由我国自主建设的一个科考站，它位于冰穹A西南方向上，海拔高达4087米，超越了俄罗斯的东方站，是海拔最高的南极科考站。 冰穹A是南极冰盖的最高点，它的海拔达到了4093米，与拉萨当雄县相当。这里环境十分恶劣，常年极寒天气。2005年，我国科考队员张胜凯登上了冰穹A，成为了登上这里的第一人。 南极之所以是平均海拔最高的大洲，主要原因就在于它的冰盖。南极冰盖平均厚度在2000米以上，它使得南极变成了一个白色的高原。 东方站由苏联于上个世纪50年代建设，苏联解体后归俄罗斯所有。上面两个科考站是最南和最高的，俄罗斯的东方站是所以南极科考站中最冷的。1983年，苏联科学家在这里记录到了－89.2 的极端低温，创下了南极洲乃至全世界的低温记录。东方站也就成为了世界冷极。 东方站也叫沃斯托克站（Vostok Station）。vostok是俄语的英文音译，在俄语里是“东方”的意思。在离沃斯托克站不远的冰盖之下有一个沃斯托克湖。沃斯托克湖是一个冰下湖，它是世界上面积最大的冰下湖。 麦克默多站是南极洲最大的科考站，拥有200多座建筑，被称为“南极第一城”。 麦克默多站位于麦克默多湾附近，这个科考站在夏季时有超过1200名科考队员，拥有自己的港口和机场。麦克默多站也是美国其他科考站的中转站。这个科考站甚至还有自己的电视台。 麦克默多站气候比较寒冷，冬季时最低气温可以降至－50 ，即便是在夏季，最冷时也可以达到－22 。 长城站于1985年建成，是中国的第一个南极科考站。 长城站位于南极大陆北面的乔治王岛上。乔治王岛是南极洲的一个气候比较温和的地方，由于受到海洋的影响，乔治王岛比较温暖湿润，即便是在最冷的7月，这里的平均气温也只有－6 左右。乔治王岛的各月降水分配比较均匀，年降水量高达702毫米，是南极洲最湿润的地区之一。长城站选址在这里也是因为气候这一原因。 长城站是中国比较大的科考站之一，它占地面积超过了2.5平方千米，有25栋建筑，这其中还包括一个医疗站，设施非常齐全。
金色年华119
这是强大的，它是烦恼，这是注定。难以置信的成功的机器，数学物理学家称之为标准模型是一组方程，描述每一个已知形式的问题，从单个原子的最远的星系。它描述的三个四个基本部队的性质：强者，弱和电磁相互作用。它预测的结果之一另一个实验后以前所未有的精度。然而，作为强大的，因为它是标准模型是远远不够完善。其数学结构是任意的。这是充满了数值常数，似乎同样特设的。也许是最令人担忧的是，它一直抵制一切试图将过去的基本力：重力。 因此，物理学家一直在试图超越标准模型以往任何时候都因为它是把20世纪70年代。实际上，他们将打破该模型与实验数据，违背其近乎完美的方程。然后，从它的碎片，他们必须建立一个新的，更好的理论。大型强子对撞机（复合） ，一个巨大的粒子加速器在欧洲核子研究中心，欧洲粒子物理实验室附近，瑞士日内瓦，是最新试图打破标准模型-之一，许多人认为所有，但成功的保证。在庞大的能源产生将迫使粒子领域的标准模型无法贯彻。在比赛中超越现状“的复合体是迄今最喜欢的”说，弗兰克威尔茨克，一个理论家在麻省理工学院在剑桥谁赢得了2004年诺贝尔物理学奖，他的工作所依据的标准模式。 但是，复合不是唯一的。几十年来，物理学家曾试图超越标准模型的各种方法，有时加速器，有时用精密测量惊险罕见的事件，有时观察外层空间。在时间的复合体得到充分加速-它的第一批结果预计不会，至少到明年夏天（见'的阻挡对撞机' ） -一些实验组认为他们有一个战斗的机会抓住第一个奖。他们的任务将难以：标准模型是一项艰巨的一块工作，抵制一切方便和明显的攻击。打击它，实验将需要前所未有的灵敏度，众多的数据，超过一点点运气。这里破败的英雄谁觉得几年最多的任务。 Tevatron 虽然得到了复合质子加速，世界上其他重量级粒子加速器赛车打破标准模型首次。自2001年以来， Tevatron ，位于费米实验室在巴达维亚，伊利诺伊州，一直在加速质子和反质子在能源约1万亿电子伏特。 这是只有七分之一的最终能源的复合体，但总能量是不是一切在寻找新的物理学。碰撞会产生新的粒子以外的标准模型是极其罕见的，这意味着不再是一个加速器运行和更多的数据积累，更好的机会找到的东西。因此，一段时间，至少Tevatron将继续有一个数据，领先的复合体。即使是夏天到2009年， Tevatron将有几倍的数据总量超过其新的竞争对手。 已经这些数据显示出一些诱人的，如果暂时的，暗示的东西超出了标准模型。一个有偏差的测量粒子被称为奇怪的乙（布）介子。该旅馆是一个奇异夸克和反夸克底部，它是最重的所有介子。根据规则被称为电荷宇称对称性，标准模型预言的旅馆衰变以同样的方式作为其反粒子（提出的反奇怪底部和夸克） 。但是，测量两个暗示的差异及其衰变。据德米特里杰尼索夫，发言人的D -零实验在Tevatron ，这一差异可能是一个重要的线索在寻求发现。这可能预示着存在新的，充满异国情调的粒子，或的
rachelliu1
中文名： 艾斯·库伯 英文名： Ice Cube 第一个周日 First Sunday (2008) 有完没完 Are We Done Yet? (2007) 极限特工2 XXX: State of the Union (2005) 我们到了没？ Are We There Yet? (2005) Beef 2 (2004) 极速酷客 Torque (2004) 理发店2 Barbershop 2: Back in Business (2004) 班哲明传奇 All About the Benjamins (2002) 又是一个星期五 Friday After Next (2002) 理发店 Barbershop (2002) 火星恶灵 Ghosts of Mars (2001) 下个周五 Next Friday (2000) Up In Smoke Tour (2000) 三个好汉 Three Kings (1999) Thicker Than Water (1999) 狂蟒之灾 Anaconda (1997) Dangerous Ground (1997) 星期五 Friday (1995) 擅入 Trespass (1992) 街区男孩 Boyz N the Hood (1991)【导演作品】 玩家俱乐部 Players Club, The (1998)
