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# 李淼的博客

## 惯性参照系

Published: Mon, 20 Nov 2017 03:01:37 +0800

Last Build Date: Mon, 20 Nov 2017 03:01:37 +0800

<潞西本地办假行驶证X>

Sun, 12 Nov 2017 14:34:07 +0800

<大理本地办假行驶证4>

Sun, 12 Nov 2017 14:29:12 +0800

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Sat, 9 Jan 2010 14:52:59 +0800

（《新发现》专栏，勿转）

Gross在他最近的公众报告《理论在科学中扮演的角色》中说，实验家往往会嫉妒理论家，因为理论家们不干脏活，却得到了最大的荣誉。这是因为，不 论你实验家实验做了多少，最后你需要一个理论或理论体系来解释它们，预言它们。牛顿做了很多实验，例如著名的三棱镜实验，但为他获得后辈的最多尊敬的还是 他的力学体系和万有引力理论。麦克斯韦也做过实验，但他的电磁理论使他不朽。我们可以一直罗列下去，爱因斯坦的相对论，玻尔和海森伯等人的量子论和量子力 学。同样，达尔文为他的进化论做了很多观察和采集，但大家最先想到的是他的理论。所以，在某种意义上，我们说最大的荣誉归于理论家是正确的。

Tue, 29 Dec 2009 16:00:48 +0800

More studies on Metamaterials Mimicking de Sitter

Casimir Energy, Holographic Dark Energy and Electromagnetic Metamaterial Mimicking de Sitter

(image)

Transformation optics that mimics the system outside a Schwarzschild black hole

Comparison of dark energy models: A perspective from the latest observational data

1、宇宙学常数；2、w常数的暗能量；3、CPL参数化；4、推广的Chaplygin气体；5、全息暗能量；6、agegraphic暗能量；7、Ricci暗能量；8、DGP模型；9、DGP唯象推广。

Sat, 26 Dec 2009 21:06:42 +0800

Verlinde今年的两篇文章是

A Black Hole Levitron

Holographic Neutron Stars

(image)

(image)

Mon, 21 Dec 2009 15:00:33 +0800

CDMS的论文已经在arXiv贴出，但估计要下礼拜一或礼拜二才能看到。摘要为：

We report results from a blind analysis of the nal data taken with the Cryogenic Dark Matter
Search experiment (CDMS II) at the Soudan Underground Laboratory, Minnesota, USA. A total
raw exposure of 612 kg-days was analyzed for this work. We observed two events in the signal region;
based on our background estimate, the probability of observing two or more background events is
23%. These data set an upper limit on the Weakly Interacting Massive Particle (WIMP)-nucleon
elastic-scattering spin-independent cross-section of 7:0 × 10..44 cm 2 for a WIMP of mass 70 GeV/c2
at the 90% con dence level. Combining this result with all previous CDMS II data gives an upper
limit on the WIMP-nucleon spin-independent cross-section of 3:8 × 10..44 cm 2 for a WIMP of mass
70 GeV/c2 . We also exclude new parameter space in recently proposed inelastic dark matter models.

Tommaso Dorigo在他的博文中说，虽然这些结果没有新物理，但说明LHC机器和研究人员都在完美的工作状态。

I was especially pleased to see that the effort of the small group of physicists from Padova and Cyprus which my colleague Franco and I have managed to put together has not been vain. We have been working day and night in the last two weeks, in order to produce an approved signal of the(image) meson. The (image) is a electrically neutral hadron, composed of a strange-antistrange quark pair. It is a very well-known particle; it was discovered in the fifties and we know everything about it, but it is worthwhile to search its decay: it is a very good calibration line on which to test the detector performance, for a couple of reasons.

Dorigo的全文：First LHC Results!

Sat, 19 Dec 2009 16:59:16 +0800

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Wed, 16 Dec 2009 17:28:08 +0800

《哈利·波特》里出现过魔法隐身斗篷，那时还是科学幻想甚至是神话，现在，利用超颖材料，人们在一定程度上实现了隐身斗篷。当然，以目前超颖材料的发展程度，我们离制造出实用的隐身衣还很远。而以这个领域的发展速度，我们可以想象不远的未来能够做出有实用价值的隐身材料。

（《环球科学》专栏，勿转）

Sun, 13 Dec 2009 14:22:14 +0800

1、一个具有纪念意义，但并没有实质意义的事情是，LHC在12月8号实现了两束相对运动的能量为1.18tev质子束。ATLAS展示了一个含有两个喷注的事例：2-jets event at 2.36Tev，这个能量超过了Tevatron。 Tommaso Dorigo写道 Well, as you know I cannot say anything about internal matters of the CMS experiment at the LHC, but I know that other sites will have information pretty soon on the matter. So my advice for tonight is to browse the web, and possibly the site of less discreet bloggers than myself. The CERN twitter feed might also be a good idea… All I can say is that LHC is working like a charm these days! CERN的 twitterfeed没有说什么。 2、当然，另一件吸引眼球的事件是关于暗物质的谣言，我上次写博客时在comment里提了。 现在再转一个Sean Carroll的说法。 Not too much point in speculating — we’ll find out next week! There was some misplaced excitement about a Nature paper, but it is true that CDMS has scheduled simultaneous talks at CERN, Fermilab, SLAC, and elsewhere. Steinn did the citizen-journalist detective work and dug up the abstract for Priscilla Cushman’s talk at CERN: I will present new results from the recent blind analysis of 612-kg days (before cuts) of data using the CDMS germanium detectors at Soudan. CDMS uses ionization and athermal phonon signals to discriminate between candidate (nuclear recoil) and background (electron recoil) events in Ge crystals cooled to ~ 50 mK. Timing, yield and position information allows us to tune our expected background leakage into the signal region to 0.5 events. I will report on what we saw when we “opened the box”, whether we have seen WIMPs or not, and implications for future dark matter direct experiments. It would seem unlikely to me that CDMS would be able to announce a cut-and-dried discovery of dark matter; that would require collecting an awful lot of data. (But what do I know?) It’s more plausible that they would see some kind of provocative signal, but without quite enough significance to be definitive. With many different competing experiments, several of which have been working for quite some time now, it seems like the kind of result that you would gradually sneak up on, rather than dramatically capture in one fell swoop. Or maybe they’re just updating us on their best limits, and some rumor-mongering has spiraled a bit out of control. We’ll see. Adrian Cho表示谨慎的怀疑： In January, however, the CDMS collaboration also published results from data taken with the same array from October 2006 to July 2007 and saw no evidence for WIMPS, says Richard Gaitskell, a physicist at Brown University. Since then, he estimates, CDMS has taken about enough data to double its sensitivity. If so, the researchers probably haven’t seen a signal so strong that it couldn’t have resulted from a few background events. “You’d be lucky to see one event,” Gaitskell says. “It’s just not enough of an increase in sensitivity to have one of these ‘Oh my God!’ moments.” The researchers might have a shot at incontrovertible sighting of dark matter had they taken enough data to increase their sensitivity by a factor of 10, he says. Still, researchers say that searching for dark matter in this way makes perfect sense–Gaitskell himself is working on such an experiment–and many hope such efforts will pay off within years. Whatever it might be, the rumored CDMS signal could be a hint of more decisive observations to come. But in all likelihood, it won’t by itself be enough convince physicists that dark matter has been spotted. 3、变换光学。 英文学名是transformation optics。我过去提到很多次了，就是和隐身斗篷、[...]

Sun, 6 Dec 2009 18:19:56 +0800

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LHC，我们期待什么?

Thu, 3 Dec 2009 02:05:11 +0800

（《新发现》专栏，勿转）

LHC，全球关心所谓宇宙秘密的人，总是被它的新闻所吸引。去年9月10号，LHC第一次启动，经过一段时间的运转，9月19号因为冷却系统的故障 53个磁铁损坏了，LHC被迫关闭。修复是一个漫长的过程，因为还涉及到整个系统的检查、清理和调试。经过一年多的辛苦工作，LHC终于在今年11月21 号重新启动。到了24号，LHC的四个探测器都检测到相反运动的两个粒子束的碰撞，这些粒子束含的是质子，每个质子的能量达到450京电子伏（1京=10 亿）。这个能量当然还远远低于设计的七千京电子伏。到了11月30号，一个纪录产生了，被加速后的每个质子的能量达到1180京电子伏，超过了过去的纪录 980京电子伏（美国国立费米实验室的纪录）。

11月29号，我开始在博客上写LHC日志，不定期登出，无非将欧洲核子中心自己发放的消息按日期列出来，只列我以为是重要的。我的第一篇日志就是 从11月21号列到11月27号，那一天欧洲核子中心加速器和技术部主任Steven Myers接受记者采访，视频登在欧洲核子中心的主页上。LHC类似的宣传非常多。我的一位朋友告诉我，在欧洲，LHC和媒体的成功互动已经被媒体学术界 列为典范。

LHC日志（1）

Sun, 29 Nov 2009 16:25:13 +0800

Credits: 所有消息来自 Antonella的tweets。

11月21日，It’s 12:24 in Geneva, operators are checking various parameters in the injection chain and the LHC #CERN #LHC。

Some info about how we make beams for the LHC:protons are produced by stripping electrons from hydrogen atoms.This is easy.Then，2nd step: protons are accelerated in a LINAC=linear accelerator. Their energy starts to increase. And then，3rd step: protons are sent to circular accelerators (PSB and PS): it’s were bunches are prepared. The energy increases. And then，4 step: protons are sent to SPS, the last circle before the LHC.A few turns to increase the energy up to 450GeV. Do you know how much is it? Back to450GeV,the extraction energy from SPS.Crushing a nut easily involves more than 450GeV of your energy.So,where is the trick?

11月21日，the LHC is preparing for injection from the SPS. ALICE experiment records splashes as well!

Nice animation of a beam splash in the LHCb experiment. Look at their page

11月22日，The anticlockwise beam is now in and circulating… working on improving the beam lifetime.

11月23日，Good morning from CERN. Over three days, the LHC has had two beams circulating with good lifetimes. It’s a good solid start.

11月24日，It’s been an eventful day at CERN. It started with two circulating beams and ended with first collisions in four detectors.

CERN’s press release has pictures of some of the first collisions

The LHC accelerated a beam to 540 GeV overnight. Here are the pictures

Fri, 27 Nov 2009 23:27:28 +0800

116. 上一次写杂博，还是今年三月份。

117. 最近买了几本书，包括《保罗·策兰》传。

118. 礼拜四晚上看了《2012》。

119. 关于诗歌。海子在他的时代是独行者，他的语言风格和意象影响了后来很多人。

80年代的一些诗歌作者现在喜欢创造双关语，如大仙。但双关语毕竟是语言游戏，供一笑而已。策兰年轻的时候也短暂地玩过双关语。

120. 其实诗歌也是人们不得已退而求其次的办法，很多事物，是不可言说的。

121. 唯有用母语才能道出真实。这是一句类似策兰说出来的话。

Thu, 26 Nov 2009 22:46:18 +0800

122. 有人去了深圳，有人在MSN上签名今夜阳光灿烂。

123. 明天要和台湾的王道还老师，微软的张铮老师见面吃饭，只好将组会移到今天。

124. 我的俄罗斯博士后Oleg Evnin同学是个很健谈的青年。

Oleg学过一些中文，我在他来之前就知道这个。我不知道的是，他的中文老师是将北岛《蓝房子》翻译成英文的人，这样Olge阅读过《蓝房子》，还 见过北岛本人。Oleg告诉我，北岛表达了对布罗茨基的不喜欢，其实北岛似乎在《午夜之门》中也表达过不喜欢布罗茨基。Oleg说布罗茨基的诗歌非常好， 可惜我没有读过。

125. 我对Oleg说起我偶尔写诗，而且还写自己风格的汉俳。

Oleg说他能读一点儿日文，也知道日本俳句里有季语的事。有人责备我写俳句不用季语，我的回答是我写自己风格的，其实日本现代俳句也有很多打破规矩的。

126. 今天讨论LHC启动的事，讨论理论所在今后两三年中应该做些什么。

127. 今天北京的天气是阴霾的天气。

Sat, 21 Nov 2009 16:04:33 +0800

(image)

(image)

Mike Douglas重新考虑了弦论在宇宙学中的有效势能问题。一直以来，多数人以为通常的有效场论分析是正确的，但这忽略了弦论中无限多个重粒子的贡献。

We define an effective potential describing all massless and massive modes in the supergravity limit of string/M theory compactification which is valid off-shell, i.e. without imposing the equations of motion. If we neglect the warp factor, it is unbounded below, as is the case for the action in Euclidean quantum gravity. By study of the constraint which determines the warp factor, we solve this problem, obtaining a physically satisfying and tractable description of the dynamics of the warp factor.

Cosmological observables are used to construct cosmological models. Since cosmological observations are limited to the light cone, a fixed number of observables (even measured to arbitrary accuracy) may not uniquely determine a cosmological model without additional assumptions or considerations. A prescription for constructing a spherically symmetric, inhomogeneous cosmological model that exactly reproduces the luminosity-distance as a function of redshift and the light-cone mass density as a function of redshift of a $\Lambda$CDM model is employed to gain insight into how an inhomogeneous cosmological model might mimic dark energy models.

Thu, 19 Nov 2009 15:24:33 +0800

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Mon, 16 Nov 2009 17:24:24 +0800

——这阳光和喧哗轮番上阵的山林

Thu, 12 Nov 2009 22:47:46 +0800

（《新发现》专栏，勿转）

Casimir-Lifshitz力与两块板之间的距离的四次方成反比，这是因为两块板之间的能量密度与距离的四次方成反比，和宇宙中的暗能量完全 不同。观测数据告诉我们，宇宙中的能量密度与宇宙大小的平方成反比，总能量与宇宙的尺度成正比。假如我们设计一种所谓超颖材料来模拟宇宙，那么超颖材料的 能量密度也应该和该材料的大小的平方成反比，总能量与材料的大小成正比，而且与Casimir能量不同的是，这个真空能应该是正的而不是负的！

Sun, 8 Nov 2009 14:18:08 +0800

1、隐身斗篷的故事 电磁隐身斗篷现在成了热门研究领域。 我受葛墨林老师的影响关注这个方向，最后终于和苗荣欣、庞毅建议用metamaterials模拟宇宙，特别是de Sitter空间。 Invisibility Uncloaked是一篇较长的讲这个故事的文章。 它从Leonhardt如何将一篇建议共形变换研究隐身斗篷的文章投到Science，Nature， PRL的故事开始（开头是悲剧，最后是喜剧），一直谈到最近的进展。 摘录： Leonhardt’s role in the cloaking field’s rise to respectability did not get off to an encouraging start. The details of his initial frustration and eventual triumph illustrate the swiftness with which the field entered the mainstream — even surprising some experts. “I began my work at a time when invisibility was not fashionable at all,” he says. That was about a decade ago. After years of quiet work with a few colleagues, he wrote a paper titled “Optical conformal mapping.” The abstract’s first words come right to the point: “An invisibility device should guide light around an object as if nothing were there.” 这一段说隐身斗篷如何迅速成为研究主流的。 我希望用超颖材料模拟宇宙学也迅速进入大家视野。 2、LHC要加速面包？ 当然不是。 在帮助LHC制冷的设备中，人们发现了一坨面包，致使LHC暂时停顿。 有人故意捣乱吗？不知道。 Efforts to get the Large Hadron Collider up and running just encountered a temporary snag, reports yesterday’s online edition of The Times of London. A crusty chunk of bread “paralysed a high voltage installation that should have been powering the cooling unit.” That cryogenic facility, guarded by high-security fences, is designed to super-chill the LHC to temperatures approaching absolute zero. And the official explanation for the out-of-place chunk of starch? “Nobody knows,” a spokewoman for the CERN particle physics laboratory in Geneva told The Times. “The best guess is that it was dropped by a bird, either that or it was thrown out of a passing aeroplane.” Then again, that doesn’t seem to quite comport with the news organization’s explanation about where the bread was found: on an electrical connection inside one of eight above-ground buildings at the site. 以上是Large Hadron Collider suffers carb attack的全文。 3、计算动物智力 动物的智力能计算吗？可能。Calculating Animal Intelligence告诉我们John Evans找到一个公式。 John’s formula is simple: C (complexity) = logN * (1 + 2logZ) where N is the number of units and Z is the average number of interactions. (If you would like to see his logic, you can read the paper cited below.) In the paper, we tested the formula by calculating C for the nervous systems of animals ranging from nematodes (N = 302 neurons, Z ~ 10) through insects and frogs and finally a series of mammalian brains. 4、人生的意义 越来越多的人怀疑人生，不知道人活着为了什么？有人说是为了自私的基因，有人说是为了生产更多的生命。 The purpose of life的作者认为生命的目的其实更加无私，是为了保护更多的生命。例如他说 The process at work is the universal tendency of all life to produce, protect, and nurture life. Differences between life forms do not seem to affect this tendency. We humans for example, like to keep pets and nurture plants not just because we enjoy doing so - we feel a need to have o[...]

Fri, 6 Nov 2009 11:08:56 +0800

(image)

Using the gauge/gravity duality, we compute the leading order hadronic (HLO) contribution to the anomalous magnetic moment of muon, amu(HLO). Holographic renormalization is used to obtain a finite vacuum polarization. We find (image) in AdS/QCD with two light flavors, which is compared with the currently revised BABAR data estimated from e^+ e^- -> pi^+ pi^- events, (image) .

I address the question whether the origin of the observed arrow of time can be derived from quantum cosmology. After a general discussion of entropy in cosmology and some numerical estimates, I give a brief introduction into quantum geometrodynamics and argue that this may provide a sufficient framework for studying this question. I then show that a natural boundary condition of low initial entropy can be imposed on the universal wave function. The arrow of time is then correlated with the size of the Universe and emerges from an increasing amount of decoherence due to entanglement with unobserved degrees of freedom. Remarks are also made concerning the arrow of time in multiverse pictures and scenarios motivated by dark energy.

Mon, 2 Nov 2009 00:36:38 +0800

（这是我为理论物理前沿重点实验室方向二写的一个研究提纲，将在某杂志发表） （刚刚结束和豆友的互动，这里：世界的脉搏是琴弦） 场论作为粒子物理和凝聚态物理的基本研究工具，已经有近80年历史。场论方法，已经渗透到物理的几乎所有领域：高能粒子物理，核物理，宇宙学，凝聚态物理，等等。场论发展到今天，经历了可重正性的要求，重正化群的发展，以及强弱对偶的深入理解，已经是一个非常成熟的工具。 在粒子物理和基本相互作用中，场论不仅仅是工具，也是一种原理性的理论，综合了量子力学和狭义相对论。实验上，到今天为止还没有发现有场论不能涵盖 的物理现象，没有出现与场论的基础量子力学和狭义相对论矛盾的任何例子。也许，自然界的确可以用场论来描述一切，也许，有一天我们会被迫超越场论。今天， 如果说还有一个潜在与场论冲突的现象，就是宇宙学常数或暗能量的存在。至少到目前为止，人们还不能用场论解释暗能量的大小和性质。 弦论也有40年历史。弦论最初起源于对强相互作用的研究，到了70年代中期，人们发现弦论自然地包含引力。如果弦论中不存在紫外发散，是有限的，那 么弦论就是一个自洽的量子引力理论。虽然弦论的有限性还没有一个严格的证明，很多迹象表明弦论的确是有限的。从弦论成为统一量子引力和其他相互作用的候选 者以来，经过了几次发展阶段，第一个阶段可以看成是量子引力阶段，第二个阶段是统一理论阶段，而现在已经进入了一个新阶段：成为粒子物理、宇宙学、数学和 凝聚态物理的辅助手段以及重要的思想来源之一。 弦论的第一个阶段和第二个阶段是混合的。作为统一理论的弦论，必须有解释粒子标准模型中的结构和参数的能力。上世纪末到本世纪初，为了这个目的发展 出来的弦景观（string landscape）看上去与这个目标背道而驰。在弦景观图像中，存在很多（可能是无限）个时空亚稳态，在给定的亚稳态中，宇宙学常数、规范群、规范耦合 常数、粒子质量都是可变的。人们需要借助人择原理来挑选某个亚稳态来对应我们观测到的宇宙，特别是宇宙学常数。目前，这个图像存在很多争议。也许我们需要 找到一些第一原理来选出一个或少数亚稳态来。 弦论迄今为止仍然没有对粒子物理的确切预言，但人们期望LHC可能会发现与弦论相关的现象。类似地，弦论也没有宇宙学的确切预言，但人们依然认为宇 宙学是发现与弦论相关现象的重要领域。经过40年的发展，弦论发展了一些物理概念与数学工具，例如强耦合/弱耦合对偶，引力与量子场论的对偶，D膜动力 学，非微扰超对称量子场论，等。这些工具帮助我们深入理解了一些量子场论的性质，黑洞的统计性质，一些微分几何问题。另外，膜世界等宇宙学和粒子物理模型 也来自于弦论发展的启发。弦论仍然是一个研究的热门，和以上谈及的发展分不开。 过去十余年，人们发现无论是弦论还是其他任何逻辑自洽的量子引力理论，必须遵从一个基本原理，该原理大致说，一个包含量子引[...]

Fri, 30 Oct 2009 15:23:11 +0800

1、Lorentz对称破坏的新限制 过去一年，寻找可能的Lorentz破坏是我研究的重点之一，Fermi GLAST观测gamma暴的高能光子的可能延迟是最有可能发现Lorentz破坏的实验之一。曾经有人觉得Fermi可能看到了这种效应，看来是过分乐观了一点。最近有篇文章 Special relativity passes key test 指出Fermi的结果排除了在色散关系的线性层次上破坏Lorentz对称（能标已经超过Planck能标）。 摘要 The Fermi team used two relatively independent data analyses to conclude that Lorentz invariance had not been violated. One was the detection of a high-energy photon less than a second after the start of the burst, and the second was the existence of characteristic sharp peaks within the evolution of the burst rather than the smearing of its output that would be expected if there were a distribution in photon speeds. The researchers arrived at the same null result when studying the radiation from a gamma-ray burst detected in September last year, but could only reach about one-tenth of the Planck energy. Crucially, the shorter duration and much finer time structure of the more recent gamma-ray burst takes this null result to at least 1.2 times the Planck energy. 2、有多少宇宙？ Andrei Linde是永恒暴涨的发明人，他当然相信在我们的宇宙之外，还存在很多其他宇宙，这些宇宙的存在是解释目前我们的宇宙为什么这么大，暗能量为什么小的理 由。当然，作为一直以来倾向相信暗能量其实是全息暗能量的我来说Linde等人的多元宇宙完全是多余的垃圾-当然是超级庞大的垃圾场。 Linde最近推出一篇计算宇宙数目的文章 How many universes are in the multiverse? 文章摘要 We argue that the total number of distinguishable locally Friedmann “universes” generated by eternal inflation is proportional to the exponent of the entropy of inflationary perturbations and is limited by $e^{e^{3 N}}$, where $N$ is the number of e-folds of slow-roll post-eternal inflation. For simplest models of chaotic inflation, $N$ is approximately equal to de Sitter entropy at the end of eternal inflation; it can be exponentially large. However, not all of these universes can be observed by a local observer. We show that in the presence of a cosmological constant $\Lambda$ an observable entropy of the cosmological perturbations, as well as the entropy of usual matter, is bounded by $|\Lambda|^{-3/4}$. In the context of the string theory landscape, the overall number of different universes is expected to be exponentially greater than the total number of vacua in the landscape. We discuss the possibility that the strongest constraint on the number of distinguishable universes may be related not to the properties of the multiverse but to the properties of observers. 这里还有一篇介绍Linde等人工作的博文 the tricky business of universe counting 里面有一幅比较艺术的Linde的照片。这幅照片很像《美丽心灵》里的Nash的一幅剧照，我希望Linde同学的头脑还是清醒的。 也许我们需要等上20年才能看到多元泡泡的破灭。我希望这一天早日到来，当然，我最希望的还是实验验证暗能量其实就是Casimir能量，一种原则上可计算的能量。 说到在天上探测暗能量，最近有消息说JDEM计划又遭挫折，我是从Sean Carroll的博客[...]

Mon, 26 Oct 2009 22:31:23 +0800

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1、徐一鸿的疯狂想法

Relaxing the cosmological constant in the extreme ultra-infrared

Non-Local Modification of Gravity and the Cosmological Constant Problem

2、全息暗能量的空间曲率和相互作用的研究

Probing interaction and spatial curvature in the holographic dark energy model

In this paper we place observational constraints on the interaction and spatial curvature in the holographic dark energy model. We consider three kinds of phenomenological interactions between holographic dark energy and matter, i.e., the interaction term $Q$ is proportional to the energy densities of dark energy ($\rho_{\Lambda}$), matter ($\rho_{m}$), and matter plus dark energy ($\rho_m+\rho_{\Lambda}$). For probing the interaction and spatial curvature in the holographic dark energy model, we use the latest observational data including the type Ia supernovae (SNIa) Constitution data, the shift parameter of the cosmic microwave background (CMB) given by the five-year Wilkinson Microwave Anisotropy Probe (WMAP5) observations, and the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS). Our results show that the interaction and spatial curvature in the holographic dark energy model are both rather small. Besides, it is interesting to find that there exists significant degeneracy between the phenomenological interaction and the spatial curvature in the holographic dark energy model.

3、Michael Green成为卢卡西教授

String theorist Michael Green has been announced as the next Lucasian Professor of Mathematics at Cambridge University. Green, 63, will succeed Stephen Hawking who held the chair from 1980 before retiring last month at the age of 67 and taking up a distinguished research chair at the Perimeter Institute for Theoretical Physics in Canada.

Mon, 19 Oct 2009 18:44:56 +0800

Casimir能量是学理论物理的人都很熟悉的概念，这种能量是Casimir在1948年提出来的，10以后实验中被探测到。最典型的例子是两个 无限大的平行导电板，在两个导电板中，光子的零点涨落不同于无限大真空中的涨落，与真空对比，零点能是负的，单位体积能量与平行板的距离的四次方成反比 （量纲分析也是这个结果）。

Casimir能量也存在于任何有限的空腔中，不同于平行导体的情况，此时Casimir能量是有限的，通常与空腔大小成反比，当然能量密度也与空腔尺度的四次方成反比。

Casimir Energy, Holographic Dark Energy and Electromagnetic Metamaterial Mimicking de Sitter

“超材料（metamaterials）”：超越天然材料的自然极限（1）

Sat, 17 Oct 2009 22:21:19 +0800

1、男生理科成绩比女生好么？ 我在最近几年改变了对女生从事理科的看法。有很长一段时间我觉得男性更适合从事科学研究，从我个人的观察以及阅读H. Georgi的ppt，我觉得女生如果表面上看起来理科不如男生，那也是因为社会和心理的因素。H. Georgi在哈佛带出了不少杰出的女物理学家，最出名的就是Lisa Randall。 上面给的链接介绍了最近一篇研究论文。我摘一段这篇博文： 从实际的学习成绩来看，似乎男生更好些。在全世界范围的调查发现，男中学生的理科成绩比女生好。但不同国家理科成绩的男女差异的差别很大。比如在一项国际 数学和科学学习趋势 报告中(Trends in International Mathematics and Science Study, TIMSS)，在所研究的34个国家中有3个国家的女生的理科成绩显著高于男生。这似乎说明一些社会文化因素会影响男女生在理科成绩上的差异。 另一个因素是心理上的，即人们对性别-学科关系的看法。如果人们认为男性更适合理科而女性更适合文科，那么男生可能就会更有兴趣学习理科，从而导致成绩更 好。那么，男女生理科成绩的差异是由人们对性别-学科刻板印象造成的么？最近一篇发表在PNAS的文章研究了这个问题。 2、睡眠睡眠 还是睡眠。我老了，总是觉得缺乏睡眠对白天工作的影响是很大的，这里有两篇继续谈睡眠的文章： The Why of Sleep Sleep Gone Awry 充足的睡眠有很多好处，但为什么人需要睡眠？还有很多争论。睡眠的好处之一是 Others agree that sleep plays an important role in regulating the immune system. In fact, sleep may have evolved to improve the immune system’s ability to fight off parasites, argue Patrick McNamara of Boston University and his colleagues in the Jan. 9 BMC Evolutionary Biology. Species of animals that spend more time sleeping each day tend to have higher counts of infection-fighting white blood cells, a database analysis revealed. The more sleep on average a species gets, the fewer parasites plague its members, and the parasites that do infect longer-sleeping species are not as prevalent in their populations as parasites that sicken shorter-sleeping species. 3、超颖材料与黑洞 最近几年超颖材料（metamaterials）越来越热，从隐形斗篷到模拟引力场如黑洞。最近，中国的崔铁军等人根据Evgenii Narimanov和Alexander Kildishev的理论建议做出了模拟黑洞的超颖材料（微波波段） First black hole for light created on Earth 摘要 A theoretical design for a table-top black hole to trap light was proposed in a paper published earlier this year by Evgenii Narimanov and Alexander Kildishev of Purdue University in West Lafayette, Indiana. Their idea was to mimic the properties of a cosmological black hole, whose intense gravity bends the surrounding space-time, causing any nearby matter or radiation to follow the warped space-time and spiral inwards. …… Now Tie Jun Cui and Qiang Cheng at the Southeast University in Nanjing, China, have turned Narimanov and Kildishev’s theory into practice, and built a “black hole” for microwave frequencies. It is made of 60 annular strips of so-called “meta-m[...]

Thu, 15 Oct 2009 13:55:16 +0800

Nielsen和Ninomiya则建议，费曼的求和规则应该改成对任意复数的求和，而不仅仅是相因子。用物理学家熟悉的语言来说，每个历史的作用 量不只是一个实数，它还有一个虚部。但这个虚部在费曼的规则中体现出来的却是改变几率的实数！这个改变几率的实数依赖于整个历史。这是他们目的论的来源。

（《环球科学》专栏，勿转）

Mon, 12 Oct 2009 01:10:03 +0800

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Mon, 5 Oct 2009 22:36:08 +0800

（《新发现》专栏，勿转） 我们知道，一个科学理论从来不能完全被证明，但却可以被证伪。这是基于这个事实，即一个理论的预言可以有无限多，我们不可能一一去证实，但一个理论 的预言可能被某个实验否定从而被证伪。例如，太阳明天照常升起，谁都不会怀疑，这就是基于以往我们的经验，或者基于牛顿力学的正确性。但是，我们却永远不 能证明太阳明天照常升起，原因是我们不能逻辑地排除经验和理论中出现的偶然漏洞。 近年来，贝叶斯统计在宇宙学中甚至在理论物理中的应用越来越多，就是和上面的那个事实有关。人们常说，贝叶斯统计是一个主观概率理论，用以区别我们 在大学学习的学术上称之为或然概率理论。在通常或然概率论中，一个事件发生的概率的含义是，假如你重复做无数次实验，那么该事件发生的次数与实验次数之比 就是这个概率。而贝叶斯理论中的概率不是这样的，在贝叶斯理论中，一个事件发生的概率是我们的主观期待这个事件发生的可能性。比如，明天太阳照常升起的贝 叶斯概率应该为1。主观上，我们说明天太阳照常升起是基于我们过去的经验，尽管这些经验是有限的。从这个例子我们知道，如果经验发生变化，那么贝叶斯概率 也将发生变化，换言之，贝叶斯概率是基于有限的数据得出的数字，这个数字随着数据的增多会不断改善。 虽然我们不能证明一个理论，我们对一个理论的信心会随证据的增加变得越来越强。在我研究的领域，我们经常看到试图用增加理论复杂的办法来修改一个简 单的理论，虽然没有任何证据说明那个简单的理论有任何问题。例如，总有人不断地发明新理论来代替爱因斯坦弯曲时空的引力理论，这些新理论越来越复杂，却在 实验中找不到一点证据。提出这些新理论并非真的是怀疑爱因斯坦的理论，在我看来，基于贝叶斯推理，其实是证明爱因斯坦理论正确性的贝叶斯概率越来越大。 在传统概率论中，一个理论正确的几率只能取两个值，0或者1，要么完全是错误的，要么是正确的。但在贝叶斯理论中，一个理论的正确概率可以是0到1 之间的任何一个数。我们人类能够做的实验和收集到的实验数据总是有限的，所以，就有了在有了一定数据的前提下，某个理论的正确的概率。更加具体地，令数据 集合为D，理论为T，我们要做出在D的前提下T多大可能是正确的判断，这个概率记为。这是一个普通的条件概率，但计算起来并不容易。 当数据积累得越来越多后，我们可以利用贝叶斯定理来重新计算新的概率，这个概率会越来越大，如果数据倾向于支持理论。贝叶斯对所谓的贝叶斯统计的主要贡献是贝叶斯定理。在介绍贝叶斯定理之前，我们说一下最近为什么贝叶斯统计在宇宙学中变得重要。 在现代物理学中，决定论一直占上风，也就是说，一旦我们知道一个系统（[...]

Fri, 2 Oct 2009 22:49:28 +0800

Peebles在这篇短文中回顾了新标准宇宙学，认为我们很快就会探测到比红移(image) 更早的时期，也就是说，当宇宙比现在的宇宙小于一百亿倍的时候。

Wed, 30 Sep 2009 19:26:31 +0800

1、Planck卫星 今年五月14号Planck卫星和Herschel卫星一同发射。最近，Planck卫星已经有了第一批数据，我今天才写已经是旧闻了。 Planck卫星从8月13号开始巡天观测，做了两周，得到第一批图，例如： Planck的“first light” Planck的公众网上是这么介绍的 The ‘first light’ survey, which began on 13 August, was a two-week period during which Planck surveyed the sky continuously. It was carried out to verify the stability of the instruments and the ability to calibrate them over long periods to the exquisite accuracy needed. This survey was completed on 27 August, yielding maps of a strip of the sky, one for each of Planck’s nine frequencies. Each map is a ring, about 15° wide, stretching across the full sky. Preliminary analysis indicates that the quality of the data is excellent. Routine operations started as soon as the first light survey was completed, and surveying will now continue for at least 15 months without a break. In approximately 6 months, the first all-sky map will be assembled. Within its allotted operational life of 15 months, Planck will gather data for two complete sky maps. To fully exploit the high sensitivity of Planck, the data will require delicate adjustments and careful analysis. It promises to return a treasure trove that will keep both cosmologists and astrophysicists busy for decades to come. 对于研究宇宙学的人来说，没有比这条新闻更令人兴奋的。 2、天才与疯子 这个话题真不新鲜，梵高、海子、伽罗华…… 原来还真有基因学上的原因。 Scientific blogging 上说，neuregulin 1与神经元之间的交流活动有关，也与精神疾病有关。下面摘录一段 In the study, the researchers recruited volunteers who considered themselves to be very creative and accomplished. They underwent a battery of tests, including assessments for intelligence and creativity. To measure creativity, the volunteers were asked to respond to a series of unusual questions (for example, “Just suppose clouds had strings attached to them which hang down to earth. What would happen?”) and were scored based on the originality and flexibility of their answers. They also completed a questionnaire regarding their lifetime creative achievements before the researchers took blood samples. They say the results showed a clear link between neuregulin 1 and creativity: Volunteers with the specific variant of this gene were more likely to have higher scores on the creativity assessment and also greater lifetime creative achievements than volunteers with a different form of the gene. Kéri notes that this is the first study to show that a genetic variant associated with psychosis may have some beneficial functions. He observes that “molecular factors that are loosely associated with severe mental disorders but are present in many healthy people may have an advantage enabling us to think more creatively.” 原文 3、09年诺奖 今年诺奖将在我们的十一长假中完成，物理学奖将在十月六号发布，具体是 Physiology or Medicine - Monday, October 5, 11:30 a.m.[...]

Mon, 28 Sep 2009 16:13:13 +0800

1、哲学与宇宙学

George Ellis，如果我记得不错的话，是南非的一位教徒宇宙学家，最近在牛津过70大寿，形式是举办哲学与宇宙学讨论会。Sean Carroll去参加了，还在博客上写了不少报道。讨论会的主题是多元宇宙。

Carroll的报道从酒吧开始。Andrei Linde对一帮哲学家解释了为什么唯我论是正确的。论证如次。Schrodinger方程告诉我们，状态的变化率正比于能量。宇宙作为一个整体能量为零（Hamiltonian constraint，其实更强，是能量密度为零），所以宇宙不变化，时间不存在。当你将自己和宇宙的其余部分分开后，你的能量不为零，所以宇宙的其余部分能量不为零，宇宙开始演化。所以认识宇宙的唯一途径是将你和宇宙分开。

Philosophy and Cosmology

Philosophy and Cosmology: Day Two

Philosophy and Cosmology: Day Three

（我觉得Linde的唯我论不完全是一个玩笑。“我”代表观测者，观测者越多，能量越大，变化也越细致，就是说能够收集到的信息就越多）

How To Be Einstein Without Being A Genius

Thu, 24 Sep 2009 22:19:50 +0800

Sun, 13 Sep 2009 18:09:10 +0800

09年诺贝尔物理学奖预测

Thu, 10 Sep 2009 16:27:25 +0800

（今天教师节，我也加入中国人习惯性的合唱，祝所有老师们快乐一天 (image) 感谢那些用email问候我的同学，其中有些人也是老师了，感谢周洋等送花的同学们，好大的一束康乃馨，你们是我永远快乐的理由。另外，真心祝愿所有想成为老师的人心想事成）

（真的希望下面两位可亲的老太太之一能够获奖）

(image)

Myriam Sarachik

(image)

Mildred Dresselhaus

Mon, 7 Sep 2009 22:39:25 +0800

Fri, 4 Sep 2009 20:07:51 +0800

（《新发现》专栏，勿转）

Unruh在设想哑洞时其实希望将来可以在实验室中实现哑洞并利用它来研究黑洞蒸发，此时，被蒸发出来的粒子叫声子，就是声的的单个量子。每个声子 的能量很类似光子，与声速成正比。当声子落入哑洞时，由于哑洞中流体的速度超过声速，声子的能量是负的，而跑出来的那个声子的速度大于流体的速度，能量是 正的。这是霍金蒸发的一个形象理解。

Unruh的哑洞的概念是1981年提出来的，直到今年，哑洞才真的在实验室中实现。原因很简单，让流体的速度在某个区域大于声速并不容易。做出这 个实验的是以色列海法的一个小组，领头人是J. Steinhauer。他们利用玻色-爱因斯坦凝聚才实现了哑洞。在流体中，玻色-爱因斯坦凝聚是非常特殊的一类，其中所有组分原子都处在同一个状态中， 这样的流体叫做量子流体，因为它利用了量子性质。要使得原子都处于同一个量子状态需要两个条件，第一是所有原子的自旋是整数的，第二需要将所有原子冷却从 而它们都趋向同一个低能状态。Steinhauer等人的实验的用了铷原子，实验的关键处是让量子流体产生一个速度分布，并且让某个区域的速度大于流体的 声速。为了达到这个目的，他们为原子们设计了一个陷阱。这个陷阱很像一个喷嘴。离开喷嘴的地方，陷阱的坡度比较平缓，在喷嘴区域，陷阱的坡度变得很陡。

Tue, 1 Sep 2009 15:08:28 +0800

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