主题：【原创】中微子超光速？(修改了一些错误) -- witten1

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老大河待整

【原创】中微子超光速？(修改了一些错误)

这里在Science上的报道：外链出处；今天在CERN的正式报告链接：外链出处（选九月二十三号的那个）。这个实验做了三年，很直接的就是测中微子的TOF（Time of Flight），两地相距730公里，实验做出来的是结果是：(v-c)/c = 2.48±0.28(stat.)±0.30(sys)×10^(-5) with an overall significance of 6.0 σ(这个精度很变态).，注意即便是在误差棒的最下限仍然是超光速的，即最少比光速快5.7*10^3m/s。后面的那个链接里是今天详细的近两个小时的报告，里面详细的分析了各种可能实验误差。

一切可靠的实验结果都必需可重复，现在需要的是一个独立的重复实验看是否能再现他们的结果，如果是的话

文章链接：Measurement of the neutrino velocity with the OPERA detector in the CNGS beam

复【原创】中微子超光速？(修改了一些错误)

家园

又要有一批物理学家享受洛伦兹的感受了。哈

复【原创】中微子超光速？(修改了一些错误)

家园

据说中微子具有静止质量？

那说明相对论还真是有一个应用范围，而不是可以用于一切范围

复【原创】中微子超光速？(修改了一些错误)

家园

不太懂这个，但是猜一下

好像测的中微子的速度是1.000006倍光速？这误差也太小了吧，而且没有理论解释，感觉是测量误差。

如果相对论是错的，那么有什么粒子的速度会是1.6倍光速，16倍光速吗？

witten你能不能科普一下中微子是怎么测量的？貌似它既不带电荷，也没有质量？如果你要测它和什么东西发生反应，那么反应时间怎么估计?

复【原创】中微子超光速？(修改了一些错误)

家园

偶初中时物理老师说，谁要是能做到比光速快一点点，

那TA就是世界上最伟大的科学家。记忆犹新啊。

当时老师在讲光速最快，某同学不服，说了一句，”快一点点不行吗？“引发了老师这个回答。

复不太懂这个，但是猜一下

家园

我也很期待确认这个结论

已经说了测量误差不会影响结论了，如果确认，那么光速的限制一被打破，可以是1.000006倍，同样也可能是1.6、6倍，哇，星际旅行终于有希望了。

现在有点二十世纪初时“两朵物理学天空上的小乌云”的感觉啊，说不定新的爱因斯坦正等往外冒呢，希望有懂物理的来给讲讲。

当然，也有另外一个可能性：

智子开始行动了！

复【原创】中微子超光速？(修改了一些错误)

家园

维度，维度。可以造成物体抄近路的维度。

复不太懂这个，但是猜一下

家园

我有一个同学是做中微子测量的

不知道他愿不愿意花点时间来做些科普。我是不行了，我离开高能好多年了，如果让我来科普这，要花去我太多时间。。。。不过，一些信息可以从wiki中来了解，以下是两个可以一看的链接：

外链出处

复【原创】中微子超光速？(修改了一些错误)

家园

引一些比较精彩的评论

来自于这个blog外链出处后面的讨论,主要引了Marek Radzikowski的评论，因为我觉得相对来说他的物理图像是对的,且这些评论足以反击一些粗浅的质疑。

The idea of gravity somehow speeding up the neutrino to a faster-than-light speed also seems to be a bit of a stretch, since (1) gravity on the earth is usually considered too weak to significantly affect the results of high energy physics experiments, (2) neutrinos (if assumed to have a regular small mass) would follow a slight geodesic arc close to (& slightly more bent than) that which light would follow (if it could pass through the matter unscathed as neutrinos do), and so presumably would arrive later than light would since a regular particle's 4-velocity never can move outside the forward light cone locally. If you are suggesting that the neutrino manages to find a wormhole (or a path through extra dimensions) that conspires to give the neutrino that extra lead on the light, then that would seem even more incredible to me than the assumption of a tachyonic neutrino. The mere existence of wormholes, along with their sudden appearance at the neutrinos' precise location at the time the experiment is run, would seem to be extremely unlikely extraneous assumptions of the sort that are liable to be shaved off by Occam's razor.

CERN scientists already gave this a second look. Fermilab saw similar results 5 years ago, but CERN is the only facility with instruments precise enough for the results to be significant. They have repeated this experiment thousands of times over three years, and they would probably agree with you that they must have been wrong somewhere. We can give them the benefit of the doubt that they were exhaustive. It is only because it is such a baffling result that they are making it available for criticism from the scientific community before they publish. It is always important to remain skeptical, but not necessarily dismissive. This is a good day for physics. Hopefully more facilities will be able to obtain funding for equipment precise enough to try and repeat or invalidate the results. It's refreshing to see neutrinos suddenly become so mainstream.

This experiment was performed exhaustively by some of the most respected physicists in the world in the only facility with instrumentation as precise. Like their colleagues at Fermilab, they were not trying to show that the universal speed limit isn't what we thought it was. Also like their colleagues at Fermilab, this is not what they concluded. Instead, they obtained a result they couldn't explain. After rigorously examining their work, they made the result public to allow others to scrutinize. Rightly so because you don't just dismiss a result like this as you know. The fact that it came from CERN is significant because of the equipment involved and, yes, the credibility of the physicists working on the project. You wrongly equate this with being fallacy or appealing to authority. Obviously, their credentials have no impact on their experiment's validity, but it is absolutely fair to say that you should hear them out and get all the facts. Finally, they are not making any claims other than that this result is intriguing and . And analysis fromb= has revealed no obvious systematic errors.

复据说中微子具有静止质量？

家园

是的

测出中微子有质量的人拿了Nobel prize，那实验也做了好多年。一切理论都有适用范围，即便也许比相对论更基本的量子力学也会有一天碰到这情况。这个实验的结果如果是对的不代表相对论就是完蛋了，只是说明了我们很可能发现了一个全新的相对论不再适用的世界，这才是其巨大意义所在，想想都过去106年了，也该有一些不一样的东西了。这是自然科学研究的另一巨大魅力。

PS：几年前别的实验室也做出类似的结果，只是精度不高，这次是第一次在6\sigma的水平上测出来的。

复【原创】中微子超光速？(修改了一些错误)

家园

事先声明，我不是做中微子的

所以昨天看那个 seminar 的时候，我感受问的问题大部分是技术方面的，正如主持人之前分配提问时段时所预计的，将近一小时的问答，只有最后三四个问题是 analysis。

大部分技术问题基本上是 as is，但是至少有两个问题我还需要继续理解：

1）实验数据分析是否需要引入广义相对论？我对回答的理解是广义相对论不影响 $\delta t$ 的符号。但是我不清楚是否需要又一个Michelson-Morley 实验来确证这一点。

2) SPS 的 beam crossing extraction （50ns beam clock）是否足够可靠。回答是调制信号证明了可靠性，并且 mostlikelyhood method 确认了。希望如此，因为 trigger delay 的可能性是很小的，但是确实发生过。

复事先声明，我不是做中微子的

家园

我不是做实验的

但是对第一个问题我可以稍微说一下。地球其实是一个很好的惯性系了，加上当代的原子钟的测量时间精度到了10^(-17)以上，所以事实上引力场在这里的效应应当是可以忽略的。前面PBS兄问到单个GPS是不是可靠，我觉得是可靠的，问题应当不会出在这个地方。