博文

年终总结精选

已有 8785 次阅读 2007-12-13 23:20 |个人分类:理论物理|系统分类:科研笔记

做年终总结不是咱们中国人的专利，老外同学们一到年终也挺忙活的，只是和我们相比，他们基本是大范围里忙，我们则是层层地总结下来，总结的人烦得要死，看总结的人草草了事。我觉得在很多情况下，年终总结就像人的阑尾，人人都知道阑尾不仅多余，有时还惹麻烦，可是与生俱来，谁都不知道哪家医院可以做这切除阑尾的工作。

对我来说，07年是相对平静、相对无聊的一年，物理学和宇宙学都没有什么惊人的发现，除了一个可能的例外（这个例外我将在合适的时候专门谈谈）。看看我写出的学术文章目录，我自己都觉得平庸-也有一个例外，见下面所列个人博客十大事件的第十条。实验家没有什么发现，理论家们也出奇地平静。看看我06 年的论文目录，虽然被同行引用的不算多，我却觉得里面有几粒小珠宝-也许离真正意义上的珠宝还远，就算潘家园的精品水晶什么的吧。我在后面还会提到那些工作。

我们从网上摘录一下美国《时代》杂志评出的07年十大科学新闻。

1. 人类皮肤细胞制成干细胞
2. 人类首个个体基因组排序完成
3 .最亮超新星爆发之谜被揭开
4. 南极附近深海发现700多种海洋新物种
5. 科学家研制出人造心脏瓣膜
6.太阳系外新发现三颗行星
7.内蒙古发现最大似鸟恐龙化石
8.尘封化石揭秘现代人身世
9.世界上最年长的动物有405岁
10.现实中的超人杀手“氡”

更具体的故事见

美国《时代》评出2007年十大科学发现

《环球科学》给我寄来了他们的十大科学新闻的候选，基本上都在我的专业之外，尤其是华南虎。我这里就不公开他们的候选事件了。

翻检我在07年写的博文中提到我感兴趣的专业内的新闻，有如下十条：

1. Gary Shiu等人声称宇宙学观测可以揭示高维空间的几何，见世界是十维的。

2. 李淼同学发表博文弦论的哲学，引起热烈讨论，遂使该博文成为评论最多的博文。

3. 李淼同学对多重宇宙论发生兴趣，开始巡回演出不只一个世界，希望梦想照进现实，并与黄庆国等人发表文章驳斥了多重宇宙论的理论基础永恒暴涨论，见乱灌中，严正维护了我奥运的主题思想：同一个世界。如你所知，近来我根据伟大的宇宙革命家霍金同学的理论，进一步论证了永恒暴涨的不可能，由于时间关系，论文可能要到明年才能面世。

4.Hartle和Srednicki发表了Hartle-Srednicki判据，基本证明了很多关于人择原理的论文是错误的。

5. Witten同学宝刀未老，在6月份露了一小手，成了狮子的爪子。据说哈佛大学的Strominger等同学正在拿着放大镜研究爪子的细节。夏天出现的文章中，此文第二重要，第一重要的当然是Huang-Li-Wang 。

6. 黄孝阳同学的划时代的巨著量子文学发表，见量子。

7. 李淼同学提出21大宇宙学相关的难题，见难（2），难（3）。

8. 霍金同学当然还不想洗洗睡了，提出霍金同学的新想法。

9. 既然《无极》能被恶搞，什么不能被恶搞，恶搞例外群小意思而已。

10. 最后，Phiphy同学非常客气地通知我们，Nima Akani-Hamed正式成为她的偶像，并写了听Nima报告的心得体会。Nima同学的观点十分类似Huang-Li-Wang的观点，而HLW的文章又和我以及同学们06年一系列工作有关，所以我开头说06年自己还做了一些有益于人民的事情。鉴于Phiphy同学的私人日记在长城以外，本博全文转载她的心得体会：

Nima Arkani-Hamed may be the most famous and interesting name in the new generation of physicists. I attended his talk today in UMD, and his words are so impressive that even though I can’t understand the details, I feel deeply interested and attracted.

His title is ‘quantum gravity: possible and impossible’. In all, his purpose is to convince us that because of gravity, IR and UV are not totally decoupled as we thought before, gravity can contribute to high dimensional operators in EFT, and that not all IR effective field theory have a consistent quantum gravity theory as its UV completion, no matter it is string theory or not. The most important criteria he uses is the Weak Gravity Conjecture, which says that gravity must be the weakest long range (U(1)) force, and an effective theory should break down even below plank scale, at $gM_{pl}$ , where g is the gauge coupling, otherwise this system will decay into a black hole. A sharper form of WGC is that any matter must have $M/Q \le 1$ . So if an IR theory violate WGC, it can never find a consistent quantum gravity theory as its mother theory.

So what EFT may be on the ‘dead’ list? One most important example is the inflation models which produce gravity wave, such as chaotic inflation. If gravity wave is generated, we require that the scalar field vev must be greater than plank scale. Naively, this can be realized in a 5 dimensional model with a very small 5D gauge coupling and it seems very natural. However, no one can find it in string theory, no matter what form they tried, there is always something, such as diliton, coming out to destroy it. Is there any general reason why they failed? The answer may be yes: it violates week gravity conjecture. There is another model named ‘N-flation’, with N species of scalar field triggering inflation. It is also problematic because it violates species bound which comes from constrain of entropy of a black hole. Moreover, if considering loop correlation of G_N, we have $frac{1}{G_N} sim frac{N}{l^2}$ which also leads to violation of WGC for large N. So Nima boldly guess that we can not see gravity wave in CMB, otherwise, it will be a big crisis.

Another interesting model he talked about was Euclidean warm hole. It was proved by Coleman that warm hole theory can be a local theory with global symmetry breaking, which can be realized with axion coupling with gravity. However, as chaotic inflation, we can not find it in string theory. And the obstacle is also WGC. To realize a warm hole, we just need to find a geodesic longer than $1/M_{pl}$ , which means we have a energy scale higher than plank scale and the corresponding U(1) gauge coupling is weaker than gravity. Further, he said that if we realize it in a AdS/CFT world, it will violate unitarity of CFT, which I do not understand.

Nima also talked about some other models, checking them with WGC. Especially, he mentioned RS. He said we can not ignore the S^5 compacted in AdS_5 when we go down from string theory. Otherwise if we take a brane near the UV side with a string on it, the corresponding particle(gauge boson) will have mass $M > 1/L_{AdS}$ which can be larger than $M_{pl}$ . We need the extra-extra dimensions to ‘dilute’ the mass of the particle. I do not understand how either, too ’string’.

Nima is really a good speaker. He makes each point very clear, and goes through the details very smoothly. Speaks fast, writes faster.