物理学哲学分享 http://blog.sciencenet.cn/u/赵国求 研究员,武汉市学科带头人,专著十部,国内外发表论文六十余篇。



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IP: 218.60.51.*   [82]沈惠川   2012-2-23 15:07
BREAKING NEWS: Error Undoes Faster-Than-Light Neutrino Results

    It appears that the faster-than-light neutrino results, announced last September by the OPERA collaboration in Italy, was due to a mistake after all. A bad connection between a GPS unit and a computer may be to blame.

    Physicists had detected neutrinos travelling from the CERN laboratory in Geneva to the Gran Sasso laboratory near L’Aquila that appeared to make the trip in about 60 nanoseconds less than light speed. Many other physicists suspected that the result was due to some kind of error, given that it seems at odds with Einstein’s special theory of relativity, which says nothing can travel faster than the speed of light. That theory has been vindicated by many experiments over the decades.
    According to sources familiar with the experiment, the 60 nanoseconds discrepancy appears to come from a bad connection between a fiber optic cable that connects to the GPS receiver used to correct the timing of the neutrinos’ flight and an electronic card in a computer. After tightening the connection and then measuring the time it takes data to travel the length of the fiber, researchers found that the data arrive 60 nanoseconds earlier than assumed. Since this time is subtracted from the overall time of flight, it appears to explain the early arrival of the neutrinos. New data, however, will be needed to confirm this hypothesis.

我的回复(2012-2-23 16:48):谢谢!
IP: 222.209.238.*   [81]罗教明   2012-1-22 18:55
IP: 59.174.155.*   [80]赵国求   2012-1-3 10:48
IP: 113.142.17.*   [79]issuense   2012-1-3 01:15
IP: 87.93.93.*   [78]甘春梅   2011-12-24 01:20
IP: 59.174.153.*   [77]赵国求   2011-12-16 16:49
IP: 221.194.180.*   [76]沈惠川   2011-12-12 16:15
我的回复(2011-12-16 16:47):我碰到他了,你送的书讲了,过几天与另一本书一起给.放心.
IP: 59.174.159.*   [75]赵国求   2011-11-28 18:10
IP: 110.85.190.*   [74]zzf195712   2011-11-28 13:49
IP: 59.174.149.*   [73]赵国求   2011-11-27 11:08
IP: 221.194.180.*   [72]沈惠川   2011-11-27 09:02
IP: 220.166.197.*   [71]罗教明   2011-10-14 10:27
happy birthday to you!

我的回复(2011-10-14 12:38):谢谢!谢谢!
IP: 59.174.157.*   [70]赵国求   2011-10-9 17:02
IP: 125.39.142.*   [69]沈惠川   2011-10-9 16:34

The claim by a team of researchers in Italy that neutrinos can travel faster than the speed of light will require extra checks before being submitted to a peer-reviewed journal. That is the position of a number of researchers in the OPERA collaboration, which announced on 23 September that it had observed superluminal neutrinos travelling from the CERN particle-physics lab near Geneva to the Gran Sasso underground lab in central Italy.

The announcement made headlines around the world, since it appears to contradict Einstein's special theory of relativity. However, not everyone within OPERA was happy to release the results publicly, with several of the 30 group leaders within the 160-strong collaboration being opposed to the release of a paper on the arXiv preprint server and the accompanying seminars and press release without further tests of possible systematic errors being carried out. Now, a larger fraction of the group leaders is concerned about the paper being submitted to a research journal. One member of OPERA, who does not wish to be named, says there is a "lot of tension" within the collaboration and that up to half of the members are opposed to an immediate submission.

Precision measurements
Neutrinos are produced by accelerating protons at CERN's Super Proton Synchrotron accelerator and colliding proton bunches 10 µs in length into a graphite target, generating mesons that in turn decay into neutrinos. The 1300-tonne OPERA detector, which has been running since June 2008, measures the properties of muon neutrinos as they travel 730 km through the Earth's crust from CERN to Gran Sasso.

The experiment was originally designed to study the oscillation of muon neutrinos into tau neutrinos, but following tentative results in 2007 from the MINOS experiment in the US that showed neutrinos appearing to travel faster than light, researchers realized accurate velocity measurements could also be carried out with OPERA. Researchers installed atomic clocks at both ends of the neutrino beam to establish exactly when the neutrinos are created and detected, and used GPS-based measurements to precisely measure the length of the baseline – the velocity being derived by dividing the baseline by the time of flight.

Collecting more than 16,000 events between 2009 and 2011, the OPERA collaboration calculated that muon neutrinos arrive on average 60.7 ns earlier than they would have done had they travelled at the speed of light, which corresponds to a fractional increase over light speed of 25 parts in a million. Having accounted for a host of possible systematic errors, including uncertainties relating to the precise moment of creation and detection of the neutrinos plus errors introduced by cabling and clock synchronization, the researchers arrived at a total systematic error of 7.4 ns, comparable with the statistical error of 6.9 ns.

The OPERA collaboration calculated a confidence level of "6σ", or a one in a billion chance the result was a statistical fluke, and this persuaded most of the collaboration that the result was solid enough to publish. However, some members were worried that unknown sources of systematic error might potentially destroy the confidence level. They argued that before making an announcement, further checks should be carried out – a process that could take several months.

One such check regards the timing of the neutrinos' arrival at Gran Sasso, and involves carrying out an analysis of timing data collected by monitoring the charge, rather than the light, generated by particles passing through the detector. This analysis relies on a very precise and painstaking measurement of the length of the cabling used to collect the timing data, in order to isolate any systematic errors that may be present within the electronics or other parts of the timing system.

Another independent check involves the statistical analysis of the data collected by OPERA. The researchers are not able to track, and therefore time, individual neutrinos as they travel from Geneva to Gran Sasso, but instead they measure the temporal distribution of the protons within each bunch just before the protons hit the graphite target and then compare this with the distribution of the corresponding neutrinos as they are detected in OPERA – with the temporal offset between the two revealing the time of flight. Some members of the collaboration argue that this offsetting procedure needs to be carried out independently, in order to be sure that the temporal profile of the neutrinos leaving CERN can be inferred accurately from that of the protons that produced them.

Heated debate
Discussions about whether or not the collaboration was ready to publish took place in early September. As these discussions were quite animated, the decision was put to a vote, with collaboration spokesperson Antonio Ereditato from the University of Bern proposing that initially the research be published on arXiv while at the same time being presented in a series of scientific seminars, before later being submitted to a peer-reviewed journal. This strategy received a majority, but not a unanimous, vote. It was then left to individual researchers to sign the arXiv paper, with about 10 senior members out of a total of 170 people (including some non-official members) deciding not to do so.

There are so many things that people outside can't check. It is these things that we have to do before publishing
Caren Hagner, Hamburg University
Ereditato says that the collaboration will continue to carry out checks but will do so in parallel with the journal submission. He maintains that no-one outside the collaboration, either at the seminars or via e-mail, has yet presented "smoking guns against what we have seen" and adds that "as experimentalists we have done everything we can". However, Caren Hagner, leader of the OPERA group at Hamburg University and one of the people whose name does not appear on the arXiv paper, believes that the collaboration should carry out the extra checks before submitting the paper for peer review. "Many of the collaboration are convinced that if a mistake is subsequently found it, won't be down to OPERA," she says. "But I am not really convinced. There are so many things that people outside can't check. It is these things that we have to do before publishing."

Laura Patrizii, who is leader of OPERA's Bologna group and who did sign the preprint, clarifies the motivation of the dissenters. "It is not that people think there is a mistake that is being hidden," she says. "But since something going faster than light would kill modern physics as we know it, some researchers would feel more at ease with these independent checks."

Looking to the outside
In addition to the checks that can be carried out within the collaboration, there are also some additional checks that CERN could perform, such as using detectors downstream of the graphite target to provide a better estimate of the profile of the departing neutrinos. The MINOS experiment is also currently improving its cabling and electronics, and collaboration co-spokesperson Jenny Thomas from University College London says that new data collected with the upgraded detector combined with a better analysis of existing data could allow MINOS to largely rule out the OPERA result within the next four to six months (but not to rule it in, given that this would require a higher level of accuracy).

Giovanni Amelino-Camelia, a theoretical physicist at the University of Rome "La Sapienza", believes that a confirmed OPERA result would lead to a "revolution" within physics. But he thinks that this confirmation is unlikely, pointing out that in the history of physics there have been many experimental "alarms" suggestive of a revolution but that only a small fraction of these, such as the Michelson–Morley experiment, have been confirmed.

With OPERA in the spotlight, collaboration members also disagree about their future research programme. Luca Stanco, leader of the OPERA group from the University of Padova and one of the people who did not sign the preprint, believes that the priority now should be further investigation of the superluminal-neutrino result, rather than neutrino oscillations. Ereditato, however, says that even though the collaboration will pursue superluminal research, "the main focus will continue to be oscillations".

About the author
Edwin Cartlidge is a science writer based in Rome




IP: 125.39.142.*   [68]沈惠川   2011-10-2 17:45
IP: 125.39.142.*   [67]沈惠川   2011-9-29 15:14
我的回复(2011-10-2 09:19):'极限速度不变',表明论者承认光速不是‘极限速度’,而且小于这个‘极限速度’,我觉得这就够了。因为‘不变的光速’是相对论的逻辑起点。
IP: 218.61.21.*   [66]沈惠川   2011-9-27 17:34
有人认为有“虚质量”,我倒认为“光量子”可能有微小的质量(de Broglie就这么认为的)。
我的回复(2011-9-28 09:01):谢谢沈老师提供的分析,同意有多种可能解释选项.如同没有必要否定牛顿力学一样,相对论也没有必要否定.它们都有理论建构中的前提约定,离开了前提约定,就无法判定正确与否了.
IP: 218.61.21.*   [65]沈惠川   2011-9-27 07:20
CERN-Gran Sasso 的中微子超光速实验

发表于 2011 年 09 月 24 日 由 XXX
从昨天(09/22/2011)旁晚开始,物理界好像炸了锅,疯传一则消息:CERN (日内瓦)
和Gran Sasso  (巨岩,意大利)的中微子实验发现,中微子的传播速度超过光速!今


中的c 不是常数了 !似乎爱因斯坦就要完蛋了!

别忙着下结论,先看一下CERN 和Gran Sasso  到底干了什麼。

CERN 和Gran Sasso  两个实验室我都去过。前者拥有世界最大的粒子加速器,后者是世
界最大的地下的粒子和天体物理实验室。CERN – Gran Sasso  的中微子实验,想法很
Sasso  (图右边)。 他们 测量中微子从CERN  飞到Gran Sasso的时间,又知道,
CERN  到Gran Sasso的距离,就测得中微子的飞行速度了。

由于地球是球状的,中微子从  CERN  到Gran Sasso  的直线传播途径都在地下。中微
有许多有名的地方:勃朗峰 (阿尔卑斯山的最高峰),Piemonte  (葡萄名酒产地),
佛罗伦萨(文艺复兴的源点),Arezzo (著名电影“美丽人生”的故事背景所在地,影

中微子地下直线穿行距离732公里,根据中微子在CERN的发射时间和在Gran Sasso 接受
(299792458  米/秒)大    0.0025%。昨晚,他们的论文已在网上贴出(见arXiv:
1109.4897v1),题目是“Measurement of the neutrino velocity with the OPERA  

直到写此文的时候,同行对CERN – Gran Sasso 结果的态度,似乎持保留或观望的居多

原因之一是,它与超新星1978A 的观测结果矛盾。超新星爆发时会产生强光及中微子。
1978A爆发时,小柴昌俊,(Masatoshi Koshiba,获2002年物理诺奖 )的地下中微子实
中微子信号也不可能与光信号同时到达地球。跑得快者先到,慢者后到。而CERN –  
Gran Sasso 结果是光速度与中微子速度有10-5 的差别。果如此,光信号将比中微子信

所以,还不忙接受CERN – Gran Sasso 的结果。

等等看, CERN – Gran Sasso 的中微子实验结果能否被其他独立的实验证实。日本的


1987年,Gran Sasso 实验室正在建设时,我去过一次。Gran Sasso 实验室建在Gran  
Sasso 山底部。它由三个大山洞组成。山洞之间有隧道相通。与外界联系也是隧道  (

Gran Sasso 实验室由意大利修公路的公司承建。意大利的高速公路,山洞极多。给实验

2006 年,当CERN  – Gran Sasso  中微子实验在建设时,我又去过 Gran Sasso  (图
3)。从照片可以看到山洞实验大厅的规模,CERN-Gran Sasso 中微子实验的终端探测器
OPERA (The Oscillation Project with Emulsion-tRacking Apparatus),即建于此
大厅里。OPERA这个名字是着意取的,不懂一点威尔弟,普契尼,大概很难混进OPERA 团

Gran Sasso 是风景旅游胜地(图4)。但在    Gran Sasso实验室里工作,却极为单调
   Gran Sasso实验室,常常雇人来做单调烦闷的工作,但工资不菲。九十年代时,
Gran Sasso实验室一直雇有这类中国雇员。他们大多是中国科学院的年轻研究人员。现

9/23/ 2011,   Tucson
我的回复(2011-9-27 08:44):谢谢沈老师的资料.
IP: 220.166.194.*   [64]罗教明   2011-9-6 15:25
我的回复(2011-9-6 15:27):谢谢!月圆共赏!
IP: 222.201.155.*   [63]吴国林   2011-8-19 12:32

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