博客李淼

怎么这里有一个我的博客的镜像？

昨天天文界在传播谣言，还不止一个谣言。第一个谣言说，暗能量不是爱因斯坦的宇宙学常数，而是phantom，我对这个消息取中立态度。对于一些弦论家，这毫无疑问是坏消息，landscape，人择原理，有可能随风而去 。最可惜的是Lenny Susskind的第三次超弦革命 。不过，假如Brad Schaefer真的是对的，我是欢呼得最早的，因为弦论家就得第二次接受现实的挑战，第二次忍痛修改我们对世界的成见。不过请放心，弦论家是一群非常非常聪明的人，没有什么可以难住他们。

第二个谣言让我不舒服，传说中的宇宙弦的候选人CSL-1被肯定不是宇宙弦。这是Motl的blog上的一段话：

I received two messages about this sad news almost simultaneously - from Mark Jackson and Joe Polchinski. Guiseppe Longo (and maybe his collaborators) has downloaded the pictures from the Hubble Space Telescope, and it is “just a pair of interacting ellipticals sitting in a rather faint cluster,” not a cosmic string.

比较早怀疑CSL-1是宇宙弦的文章是这篇。

Motl的blog更新了，后来他又加了一段话：

Let me add to the main text that Joe Polchinski’s estimated probability that a cosmic string could be seen was something about 10%. Joe would have therefore told you a smaller number for this particular case, I think. In this sense, it is not a surprise that the conjecture that CSL-1 was a cosmic string was falsified. While it is not a surprise, it is still a disappointment.

A confirmation that it is a cosmic string would have meant much more obvious progress. This observation has falsified one particular case but it has not falsified the idea of cosmic strings in general. And just to be sure: it has of course told us nothing about the validity of string theory as a fundamental theory.

Motl希望的图是这样的：

这年头，研究天文、宇宙学就像在水上写字，不过，有了互联网，谣言和消息传播得和光速一样快。（以上改自张爱玲研究红楼梦中的一段话）

一段时间以来，暗能量被许多人认为可能是phantom，就是说，能量密度会随时间变得越来越大。最早从超新星数据看出这个的是Huterer和Cooray,（文章），接着张新民等人也号称看到了，并且引进了一种所谓quintom（精灵）模型（文章），我直到不久之前还将信将疑，因为phantom在理论上很难实现，需要一种不稳定标量场，当然，我的全息暗能量模型也能容纳phantom。

现在，有人声称射线爆的数据也支持一个随着时间变化而增大的暗能量了，可信度大约是97%。这是第三次有人说虎来了，我不由得相信起来。张新民私下跟我开玩笑，现在的自然科学二等奖实在没有得头，要得就得一等奖，如果暗能量果真是phantom，他倒真的有希望。我更希望我的全息暗能量是对的，哪怕是phantom

在宇宙学中，这是一个需要奇迹也产生奇迹的时代。Michael Turner在Brad Schaefer的记者招待会后说：”It’s an exciting time to be an astronomer. The mysteries run — literally — from our own back yard to the edge of the Universe.”

也许，可怕的幻影（phantom）真的来了：

（13日：刚收到张鑫的一个email：
最早从超新星数据中看出w从>-1变化到<-1的应该是Ujjaini Alam, Varun Sahni, A. A. Starobinsky的文章
astro-ph/0403687。从他们的文章的图中可以清楚看到这一点，暗能量的能量密度的演化行为是先变小再变大。
Dragan Huterer和Asantha Cooray的文章稍微晚了一点点(astro-ph/0404062)。我那天做报告时可能将他们的次序列颠倒了，呵呵。）

刚刚看到Brad Schaefer在Carroll的blog上的发言，转载如下，希望能够帮助对此感兴趣的人（这是blog帮助研究的一个好例子）

Brad Schaefer on Jan 12th, 2006 at 12:56 pm
Sean has pointed me to this blog and requested me to send along any comments that I might have. His summary at the top is reasonable.
I’d break my results into two parts. The first part is that I’m putting forward a demonstration of a new method to measure Dark Energy by means of using GRBs as standard candles out to high red shift. My work is all rather standard with most everything I’ve done just following what has been in the literature.
For this, what is new is that I am using

－－－－－－－－－－－－－－－－－－
Brad Schaefer on Jan 12th, 2006 at 1:29 pm
****Oops, this message is broken up by my accidently hitting a return after a tab. The network link here at the AAS meeting is slow and balky. The message will now be continued****

The GRB Hubble Diagram has been in print since 2003, with myself and Josh Bloom independently presenting early version in public talks as far back as 2001. Over the past year, several groups have used the GRB Hubble Diagram to starting putting constraints on cosmology. This prior work has always used only one GRB luminosity indicator (various different indicators for the various papers) and for no more than 17 GRBs (neglecting GRBs with only limits).

What I am doing new is I am using much more data and I’m directly addressing the question of the change of the Dark Energy. In all, I am using 52 GRBs and each GRB has 3-4 luminosity indicators on average. So I’ve got a lot more data. And this allows for a demonstration of the GRB Hubble Diagram as a new method.

The advantages of this new method is that it goes to high redshift, that is, it looks at the expansion history of the Universe from 1.7-6.3 in redshift. It is impervious to extinction. Also, I argue that there should be no evolution effects as the GRB luminosity indicators are based on energetics and light travel time (which should not evolve). Another advantage is that we have the data now, with the size of the data base to be doubled within two years by HETE and Swift.

One disadvantage of the GRB Hubble Diagram is that the GRBs are lower in quality than supernovae. Currently my median one sigma error bar is 2.6-times worse in comparing a single GRB and a single supernova. But just as with supernovae, I expect that the accuracy of GRB luminosities can be rapidly improved. [After all, in 1996, I was organizing debates between the gradaute students as to whether Type Ia SNe were standard candles or not.] Another substantial problem that is hard to quantify is that our knowledge of the physical processes in GRBs is not perfect (and certtainly much worse than what we know for SNe). It is rational and prudent for everyone to worry that there are hidden problems (although I now know of none). A simple historical example is how Cepheids were found to have two types with different calibrations.

So the first part of my talk was simply presenting a new method for getting the expansion histoy of the Universe from redshifts up to 6.3. For this, it is pretty confident that the method will work. Inevitably there will be improvements, new data, corrections, and all the usual changes (just as for the supernova).

The second part of my talk was to point out the first results, which I could not avoid giving. It so happens that the first results point against the Cosmological Constant. I agree with Sean that this second part should not be pushed, for various reasons. Foremost is that the result is only 2.5-sigma.

Both parts of my results are being cast onto a background where various large groups are now competing for the a new dedicated satellite.

这基本上是一篇物理学文章的题目，《Message in the Sky》，徐一鸿和另一个徐（Stephen Hsu）三个月前写的文章。Tony是个非常非常聪明的人，这一次不知道他真的收到了上帝的启示，还是认真地恶作剧一回？

他们说，如果上帝在创造世界的时候想留给我们一点关于他的启示，不会在大峡谷的岩石中留下什么痕迹，也不会在我们的基因中留下什么痕迹。最有可能的是，他在微波背景辐射涨落的功率谱上做了什么手脚，因为微波背景辐射是宇宙中任何角落的智慧动物都能够看到的。给定一个角“量子数”，角功率谱有个样本，扣掉不确定性，上帝在中能够给我们的信息量是。我们现在能够观测的上限是，这样，可以有大约bits原则上能够被我们读出。

这是一个相当大的信息量，两位徐先生说，上帝可以告诉我们大统一的群是什么，等等。

老实说，虽然大部分人会将这样的想法当着科幻来看，如果物理原理并不禁止我们在实验室中造出另一个宇宙，他们的想法也不能被看成纯粹的胡说八道，也许有一天，一个科学疯子会成为一个新宇宙的上帝。

Note added: 桑葚告诉我们Stephen Hsu讨论过他们的文章，我去看了一下，觉得他提到Linde给他写信的那个帖子有意思，就顺手转过来。Note added to note added: 这个转帖没有征得Steve的同意。

Message from Linde
Andre Linde (Stanford) sends some interesting comments on our paper Message in the Sky. He points to an earlier paper of his, and a nice interview in Slate, where he discusses the idea of creating a universe in the lab. In the comments section of the previous post I mentioned that one of the reasons I had been thinking about this topic is the work of Farhi and Guth (MIT) on the behavior of a false vacuum bubble created in the lab. I hadn’t known that Andrei had also worked out the solution (although I should have). A false vacuum bubble can expand in a non-Euclidean way, so that the observer in the lab sees the bubble shrink while an observer inside sees it expand (inflate).

Andrei also had the idea that the creator of the bubble universe might like to send a message to its future inhabitants. He discusses tuning the fundamental parameters so that physicists in the bubble universe would understand that their physical laws had been adjusted just-so. Our proposal allows a bit more information to be encoded (or rather, read out), but the idea is similar. The problem with having special values of the constants is that some nutty physicists might come up with anthropic reasons explaining those values, and not figure out it was done intentionally

But why bother making a universe if it’s going to run away from you? Wouldn’t you want to have some power over how your creation unfolded, some way of making sure the beings that evolved in it turned out well? Linde’s picture was as unsatisfying as Voltaire’s idea of a creator who established our universe but then took no further interest in it or its creatures.

“You’ve got a point,” Linde said. “At first I imagined that the creator might be able to send information into the new universe—to teach its creatures how to behave, to help them discover what the laws of nature are, and so forth. Then I started thinking. The inflation theory says that a baby universe blows up very quickly, like a balloon, in the tiniest fraction of a second. Suppose the creator tried to write something on it surface, like ‘Please remember I created you.’ The inflationary expansion would make this message exponentially huge. The creatures in the new universe, living in a little corner of one letter, would never be able to read the whole thing.”

But then Linde thought of another channel of communication between creator and creation—the only one possible, as far as he could tell. The creator, by manipulating the cosmic seed in the right way, has the power to ordain certain physical parameters of the universe he ushers into being. So says the theory. He can determine, for example, what the numerical ratio of the electron’s mass to the proton’s will be. Such ratios, called constants of nature, look like arbitrary numbers to us: There is no obvious reason they should take one value rather than another. (Why, for instance, is the strength of gravity in our universe determined by a number with the digits 6673?) But the creator, by fixing certain values for these dozens of constants, could write a subtle message into the very structure of the universe. And, as Linde hastened to point out, such a message would be legible only to physicists.

“You might take this all as a joke,” he said, “but perhaps it is not entirely absurd. It may be the explanation for why the world we live in is so weird. On the evidence, our universe was created not by a divine being, but by a physicist hacker.”

Linde’s theory gives scientific muscle to the notion of a universe created by an intelligent being. It might be congenial to Gnostics, who believe that the material world was fashioned not by a benevolent supreme being but by an evil demiurge. More orthodox believers, on the other hand, will seek refuge in the question, “But who created the physicist hacker?” Let’s hope it’s not hackers all the way up.

参加南京大学和紫金山天文台联合粒子－核－宇宙学研究中心的成立大会。南京大学终于要有正式粒子物理研究中心了，不容易啊。

江苏是我的老家，这么富裕的省不支持粒子物理研究实在说不过去。虽然粒子物理-宇宙学不实用，像美国那样有闲钱花在这上面也是应该的。只有穷人才整天强调实用实用，所有的钱要花在锅碗瓢盆上，大款才在实用之外想到玩:-)（研究实用物理的网友请原谅一下我开这玩笑）

如果有有意思的事情发生，回来会报道一下。

博客越来越流行了，新浪的名人博客每天都在增加，博客是网络快餐文化中最新的一道，比麦当劳的麦辣鸡腿堡还要新潮。

我从科学博客得到的好处很多，我没有理论，只要简单地举几个例子。

第一个例子是最近Arkani-Hamed等人的文章。我先在arxive上看到这篇文章，其实Motl本人早几天就在自己的博客中提到了。这篇文章的内容本身就很吸引人，当Motl玩笑式地称这是弦论第三次革命让我了解到这几个作者对这篇文章的态度，毫无疑问，如果这个结果是正确的话，这篇文章将会有很大的影响。不瞒大家，除了我自己外，我已经让两个学生投入精力看看我们能够做什么。

如果更多的人能够像Motl那样在博客上公开讨论自己的、别人的工作，Harvard就不再局限在Cambridge一角，就会扩大它的圈子，Princeton小组也会成为一个更加大的virtual小组。

第二个例子是我通过Carroll等人对Brockman的World Question Center最新一轮的dangerous questions的评价了解到一些“思想者”的“深刻思考”，和Carroll等人的看法。我自己很少浏览那些网站直接看这些人的dangerous questions。 我看到P. Anderson继续做宇宙学的鸵鸟，认为暗能量不存在；Martin Rees继续着科学的噩梦；Lenny Susskind认为人择原理将像癌症一样扩散（我好像听到了上帝的笑声-_-）；我们可爱的朋友Lee Smolin认为达尔文的进化论和爱因斯坦的广义相对论是类似的理论：都是不依赖背景的理论（我因此得知Lee在哲学家的道路上越走越远）。当然，从Carroll和Motl的态度我知道了Carroll是美国主流知识分子－左派，而Motl是终于走出东欧最终蜕变的右派。不过，感谢这些博客们，感谢这些思想者们，让我在一天无聊的时候陷入沉思，做了一回哲学家-_-

第三个例子也许更为重要，我通过一些博客了解到一些学物理的学生在写博客，并且得知他们是如何学习的。

让我们祝博客将像癌症一样扩散。

现在我在电脑屏幕上打开一个窗口，看今天下载的阿森纳/曼联的比赛－今天凌晨4点的，本来想看，一不小心睡着了；同时，我打开另一个窗口，开始写今天的博客。我有时喜欢同时做两件事，甚至三件事。

工作狂这个话题在现时的中国怎么也不该是一个话题，当然民工除外。在我的同事和朋友中我没有见着一个真正的工作狂。是的，有人待在办公室的时间比我长，也有人早上起得比我早，甚至也有人晚上待在办公室，却没有一个是工作狂。

我到底想谈这个话题，是因为看了过去的一个老朋友Mark Trodden在他自己的博客中谈了这个话题，并引来不小的反响。Mark是个英国人，所以直到现在还保留着欧洲人的传统，那就是享受生活。在美国享受生活实在不容易，因为美国是个工作狂的国度。Mark写那个博客是希望他的学生学会休息，学会享受生活，不要一味地工作。他说，英国人整天想表现出来的是无所事事，虽然其实背地里也用功得要命；而美国人以整天工作为荣。同样是用功，却是两种不同的态度，不同的文化。

Mark招来很多人的反对，少工作，在美国文化中简直不可容忍。 Juan （是 Maldacena 吗？）说，美国之所以现在甚至将来是科学的领导者，就是因为工作狂的文化，怎么能教年轻人少工作呢？我是同意Mark而反对Juan的。不过，科学上卓有成就的人的确都是工作狂。Pais在《Niels Bohr’s Times》比较爱因斯坦和玻尔时写道：……两位的最重要的工作都是一个人做出来的……两位有时工作到生病为止，在爱因斯坦则更甚……，由此可见，不做工作狂不行。

但美国式的工作狂有时纯粹来自于压力：学生不写出好文章来找不到博士后位置，博士后不高产找不到教职，助理教授不出好工作拿不到tenure，教授停止工作轻则同行看不起，重则拿不到经费……总之压力来自于生存，而不是像爱因斯坦和玻尔那样来自于inner drive。

我在反对美式的工作狂同时，却提倡工作狂，一是我本人早就不是工作狂了，每天真正工作的时间少得可怜，二是我们的学生看来还是要多投入一些时间，和美国的学生比，他们绝对是在“享受”生活。不过，我不能对他们要求太多，毕竟他们的老师们没有做出什么好的榜样来（当然，我的少数同事还是比我用功的），在中国，稍微做点事，是很容易混的。最近我们这里从美国来了两个客人，其中一个告诉我，他在机场还在写文章。我拼命回忆，好像我这辈子在机场只有两次做了计算。看来我早就跟美国文化说再见了。

记得曾经有人跟我说，你知道Seiberg是怎么用功的么？你知道Strominger是怎么用功的么？我只有苦笑，这些我都知道，可是……我需要压力。

我希望中国研究科学的人将来能像欧洲的同行一样，虽然背后拼命工作，表面还装作轻松的样子。

引力当然是最弱的力。徐一鸿在《老人的玩具》中这样比较一对质子之间的电磁力和引力，将一对质子分开一厘米，它们之间的引力相当于当它们分开一光年时的电磁力。

但在两个一般的物体之间，引力不会总是这样弱。考虑一个带电的黑洞，黑洞的质量总是大于它带的电荷（取一个恰当的单位），当质量等于电荷时，这个黑洞就变成极端黑洞，两个极端黑洞之间的引力往往等于它们之间的电磁力。在弦论中，有时有很多这样的态，叫BPS态，此时BPS态的电荷同时又是一种中心荷(central charge）。

Arkani-Hamed, Motl, Nicolis和Vafa在今天的一篇文章中猜测，在任何一个自洽的引力理论中，在某种意义上，引力总是最弱的那一个。

他们的猜想的严格表述是，对于一个最轻的、稳定的带电粒子，比值，如果我们将普朗克质量设定为1。一个更为粗略的表述是，对于任何一个U(1)相互作用，总存在一个带电粒子，满足，这里是相互作用耦合常数。

这个猜想的一个引理是，如果, 对于这个U(1)相互作用，存在一个新的标度，在这个标度以上该相互作用失效。这个结果违反了有效量子场论的直观：在一个有效量子场论中，如果我们还没有达到Landau极点，那么这个U(1)相互作用总是有效的。

Arkani-Hamed等人的结果告诉我们，世界不是半经典分析甚至有效场论告诉我们的那么简单。

我们可以不相信大统一以及它预言的新的比普朗克表度略小的能标，但“弱引力猜测”告诉我们，肯定存在一个比普朗克标度略低的能标，因为弱电的耦合常数远小于1。这是“弱引力猜测”的预言。

这个猜测还告诉我们，千万不要相信那些类似loop gravity的说法，因为对于那些理论，你很容易加上一个长程力得到任意你想得到的结果。

想了半天要不要将明年和ICTP合作的string school在这里做一下宣传，这里毕竟是我个人博客，应该和任何“公事”无关。但是，也许交叉中心的那个主页很多人不知道，还是在这里做一下广告吧。

String School

credit: 交叉中心秘书汤蕙同学

过了新年，切尔西完美地完成圣诞魔鬼赛程，高兴得很，请允许我离开物理一下。

老徐是谁？猜猜。

她是当今最火的博友，过去的四小花旦之一。我一直不明白她为什么那么火，浏览了她的博客后，我明白了。