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聊聊圈量子引力 谁了解这方面可以来聊聊。我并不是这个领域的专家,所以只能也只能随便说说。每周的例会式报告,今天听了北师大”马老”的报告,感触颇多,所以随便扯几句。不过话说回来,下面听的人大多也都是弦理论、粒子物理、宇宙学等方面的专家,大多也都不了解圈量子引力,所以今天的报告也是极其科普,不过来听的人倒是蛮多。 简单聊聊圈量子引力理论我被科普的部分与弦理论的比较。圈量子引力这理论有不少人对之不屑一顾,甚至直接抨击其是民科之作,单从学术态度上来说,不应该有”罢黜百家,独尊儒术”这样的观念,学术就应该百家齐放,虽然研究圈量子的领域人数少的可怜。不过作为一个物理理论,它的出发点更倾向从广义相对论开始,慢慢的加入量子力学的味道而不像弦理论那样依托量子场论一点点加入引力的味道,显然这样的结果就是比较吃亏,因为做量子场论的人实在远大于纯做引力理论的人,所以两个理论必然人力资源分配就不会平衡。圈量子引力有一些好处,比如不需要额外的内容,只保留广义相对论和量子力学,反而这方面弦理论却引入了过多的"花样",比如额外维,超对称这样的东西,单某种程度也使得弦理论的内容更加宏大,看起来更加基本,它可以出现费米子以及时空维度等等相关的内容,而这些是圈量子引力还不能给出的。 再来看看两个理论的出发点,它们都基于广义相对论和量子力学,特别的,弦理论更多的考虑量子场论的东西。人们知道广义相对论直接量子化会出现不可重整的困难,我们仔细考察这个问题出现的原因,是因为传统量子场论对于高能紫外区域的物理并不清楚的原因,因此会出现圈图动量积分到无穷大的情况。当然处理发散,量子场论有重整化的办法。虽然重整化可以剪除一些量子理论中的发散,但量子场论也并不知道应该剪除多少”无穷大”,因为这要依赖于重整化条件,所以重整化实际上做的只是把我们不了解的量子场论的高能行为用重整化后的有效场量、耦合常数、有效质量等等等效的描述出来。所以常常说量子场论是低能有效理论。然而重整化对于引力理论却存在无法克服的技术困难,直观的一个原因是引力的耦合系数是质量量纲的负次幂(这种情况下圈图的发散是二次或者更高的发散,无法重整化),这就是常说的量子力学和广义相对论的一个严重的矛盾之处,当然也就是相对论的定域因果性和量子力学波粒二象性的分歧所在。而对于这个问题的解决,两种理论给出了不同的方案。圈量子理论选择了改造广义相对论,把它改造成类似规范场理论的东西,将正则变量改为一种联络而非度规,再以联络构造和乐来实现量子化。而弦理论的基本出发点是,基本粒子并非是点状物体,而应该有个基本尺度,然后仍然按照传统量子化的方式实现量子化。从这看来,圈量子似乎更像是做了一些技术上的改变,而弦理论则只是改变了点粒子的基本假设。 从发展状况来看,圈量子引力的成绩还没法和弦理论相提并论,因为弦理论的内容实在太多太大,尤其第二次革命发现了Ads/CFT之后,而且圈量子引力也比弦理论年轻的多。总之这理论要想继续发展还有很多路,比如它还没法给出闵氏时空的情况,因为它做的很多东西都是处于非微扰的情况,而微扰区域的物理却成了困难,这和弦理论包括一般理论的情况正好相反。暂时先这么多。
关于E8的那个TOE @foozhencheng 原文在此:arXiv:0711.0770v1 有兴趣的也可以来看看~~ 妹子说晚上不宜看书太久,于是听妹子的话,细节的内容抽几天白天的时间有空看看~今天只是大致浏览了第一和第三节的部分~~ 首先,这理论数学结构与规范场理论,或者说Yang-Mills理论很不一样。 对于Yang-Mills理论,我们知道主丛上的connection是描述规范Boson,其它Fermion是伴丛上的截面,这样主丛上的联络在结构群李代数上的变换就是按照转换函数定义的那样变换,于是它在时空上的分量实际上就是按照结构群的伴随表示变换;而伴丛的截面的分量就按照结构群的基本表示那样变换。实际上标准模型就是这样建立起来的一种Yang-Mills理论,只不过结构群选择成了SU(3)×SU(2)×U(1)。 然后看这个理论,它直接把标准模型所有粒子都是视做是主丛上的connection,并且要求Fermion依然是Gaussmann形式描述,所以这一点与Yang-Mills理论很不一样,但是与Super Yang-Mills却是类似,在Super Yang-Mills,有些Fermion也是主丛上的connection,这实际上还是把Grassmann代数引入到了主丛上,只不过Super Yang-Mills是通过对称性要求主丛上要有这种Grassmann form,然而它这里是一上来就要求所有粒子全部视作是主丛connection的一部分,虽然出发点不同,但结果都是引入了反对易代数,这就打破了No go定理的限制,为后面引入引力做了铺垫。 最后看它的作用量动能项,实际上全部用Ricci曲率来描述,实际上主丛要是Frame bundle,那么Ricci曲率就是GR里面的Ricci Tensor;如果主丛上代表不同的Yang-Mills势,那么Ricci曲率就是规范场强,实际上这都是一个方程,即Cartan structure Equation: F=dA+i[A,A] 把A当做规范场,那么F就是对应的场强;你要把A当做是克氏符,那么F就是Ricci曲率。从这一点来说,这个理论把所有的东西都放在E8主丛的connection里面反倒比一般Yang-Mills理论简单了。引力理论与Yang-Mills理论区别就在于作用量上,引力作用量是曲率的一次幂,而Yang-Mills则是二次幂;而且Fermion和Higgs要满足Dirac和K-G方程,和规范场都不一样,所以它们弄了个所谓的BF作用量,把这些粒子满足的作用量形式都凑出来~~可以说,这个作用量和一般的Yang-Mills理论以及引力理论都不一样,不过这个理论起点就已经不一样了。还有值得一提的是,宇宙学常数这里当做了Higgs的真空期待值,这等于说引力子有一个正比于宇宙学常数的质量项,你可以看3.2.1节下面那个作用量,实际上这是很多做massive gravity理论的人的想法,这里也囊括进来了。 至于第二章,那个主要是告诉你如何从E8群一点一点把标准模型的对称性和粒子约化出来的,那些图都是粒子物理上常用的寻找粒子态的权图,E8这个群很大,所以权图很麻烦,怎么约出来的这是细节问题,有时间再看~不过E8低能下破缺到标注模型对称群可以说做出这个来一点不稀奇,因为E8李代数是248维,而标准模型的李代数只有12维,所以这么大的群破缺/约化到这么小的群上不难相信肯定有办法,甚至办法都不唯一。所以这些细节可以慢慢看~~ 先暂时这么多,想起来别的再说~另外白天有时间也再看看~~
【简介】弦理论(不是科普) 最近去给别人讲物理,最后讲到了弦理论,正好拿来也分享一下~~这不属于科普,属于简介~~ 翻译自:KATRIN BECKER,MELANIE BECKER,JOHN H. SCHWARZ;String and M-Theory A Modern Introduction 1.1历史起源: 弦理论产生于二十世纪六十年代末期,当时是为了描述强核力的作用形式。这种相互作用是存在于原子核内部,把中子和质子构成原子核的力,类似于把夸克束缚在质子或者中子内部的相互作用一样。弦理论是基于一种一维延展称作弦(String)的物体,而不是传统的把基本粒子视作点粒子的理论,进而可以达到描述粒子(重子)间强核力以及强相互作用的行为。 用弦模型描述强相互作用的基本想法是:不同的粒子(或者说量子态)对应于弦的不同振动模式(激发态)。这个观点给出了一个令人满意的统一的图像,因为它可以用一个单一的基本物体(弦)来描述各种各样的强子的产生以及相互作用,如Fig 1.1所示:Fig1.1 不同的粒子对应于弦的不同激发态) 在二十世纪七十年代,另一种用于描述强相互作用的理论,称之为量子色动力学(Quantum Chromodynamics or QCD for short)的理论被发展起来。它带来的一个结果就是弦理论基本被人们抛弃了,当然这也和当时的弦理论存在的很多技术上难以克服的问题有关。人们普遍认为QCD是非常有价值的理论,因此它开始成为研究的热门领域。而对于弦理论,虽然说人们今天已经对弦理论有了比当时深入多的理解,但如何用它去具体描述强相互作用依然是不清楚的。 后来,弦理论被证明出来它是一个更宏伟的理论,因为对它的量子理论的研究发现它可以统一的描述引力和自然界其他(三种)基本相互作用。原则上说,它有潜质成为一套完整的用于统一理解基本粒子相互作用和宇宙演化的理论。虽然这还是一个遥远的梦,但现在已经很清楚的看到,惊喜总是不断的从这个使人的迷理论中涌现出来。
【简介】弦理论 摘自:KATRIN BECKER,MELANIE BECKER,JOHN H. SCHWARZ;String and M-Theory A Modern Introduction 弦理论产生于二十世纪六十年代末期,当时是为了描述强核力的作用形式。这种相互作用是存在于原子核内部,把中子和质子构成原子核的力,就类似于把夸克束缚在质子或者中子内部的相互作用一样。弦理论是基于一种一维延展物体,称作弦(String)的物体,而不是传统的把基本粒子是做点粒子的理论,进而可以达到描述粒子(重子)间强核力以及强相互作用的行为。 用弦模型描述强相互作用的基本想法是,不同的粒子(或者说量子态)对应于弦的不同振动模式(激发态)。这个观点给出了一个令人满意的统一的图像,因为它可以用一个单一的基本物体(弦)来描述各种各样的强子的产生以及相互作用,如Fig 1.1所示:(Fig1.1 不同的粒子对应于弦的不同激发态) 在二十世纪七十年代,另一种用于描述强相互作用的理论,称之为量子色动力学(Quantum Chromodynamics or QCD for short)被发展起来。它带来的一个结果就是弦理论基本被人们抛弃了,当然这也和当时的弦理论存在的很多技术上难以克服的问题有关。人们普遍认为QCD是非常有价值的理论,因此它也成为研究的热门领域。而对于弦理论,虽然说人们今天已经对弦理论有了比当时深入多的理解,但如何用它去具体描述强相互作用依然是不清楚的。 弦理论被证明出来它是一个更宏伟的理论,因为对它的量子性质的研究发现它可以统一的描述引力和自然界其他(三种)基本相互作用。原则上说,它有潜质成为一套完整的用于统一理解基本粒子相互作用和宇宙演化的理论。虽然这还是一个遥远的梦,但现在已经很清楚的看到,惊喜总是不断的从这个使人着迷理论里面涌现。
【歌剧】The phantom of the opera(Instrumental Played by us) Keyboards:CloudK Guitar& Bass :Spirit.Lu o Drum hit:某渣渣 视频来自:http://tieba.baidu.com/mo/q/checkurl?url=http%3A%2F%2Fwww.tudou.com%2Fprograms%2Fview%2FIKFcmCxgm-Q%2F&urlrefer=e3dc1874fe88cd9d77d0a159074c3223 原唱: Sarah Brightman 歌词: Christine: In sleep he sang to me, In dreams he came. That voice which calls to me, And speaks my name And do I dream again? For now I find, The phantom of the opera is there, Inside my mind Phantom: Sing once again with me, Our strange duet. My power over you, Grows stronger yet. And though you turn from me, To glance behind. The Phantom of the Opera is there, Inside your mind. Christine: Those who have seen your face, Draw back in fear. I am the mask you wear. Phantom: It's me they hear. Both: Your/my spirit and my/your voice, In one combined. The Phantom of the Opera is here/there Inside your/my mind/heart. Offstage: He's there, the Phantom of the Opera! Beware, The Phantom of The Opera! Phantom: In all your fantasies you always knew that man and mystery Christine: Were both in you Both: and in this labyrinth where night is blind the phantom of the opera is there/here inside your/my mind/heart. Phantom: Sing my Angel of Music Christine: He's there, The Phantom of the Opera! (Vocalizing) Phantom: Sing! Christine: (Vocalizing higher) Phantom: Sing for me! Christine: (Vocalizing higher) Phantom: Sing my angel of music! Christine: (Sings higher) Phantom: SING FOR ME! Phantom: I have brought you, To the seat of sweet music's throne. To this kingdom where all must pay homage to music, Music. You have come here. For one purpose and one alone. Since the moment I first heard you sing, I have needed you with me to serve me, to sing, For my music. My music
【Rock】Over the hills and Far Away(Played by us) Keyboards:CloudK Guitar:Spirit.Luo Bass:M.Jin(客串) Drum hit:某渣渣 视频来自:http://tieba.baidu.com/mo/q/checkurl?url=http%3A%2F%2Fwww.tudou.com%2Fprograms%2Fview%2FogqXf1lK5kI%2F&urlrefer=9e6bb7c9d8c9efff19bc8bdb07617cbd 原唱:GaryMoore 歌词: They came for him one winter's night. Arrested, he was bound. They said there'd been a robbery, his pistol had been found. They marched him to the station house, he waited for the dawn. And as they led him to the dock, he knew that he'd been wronged. "You stand accused of robbery," he heard the bailiff say. He knew without an alibi, tomorrow's light would mourn his freedom. Over the hills and far away, for ten long years he'll count the days. Over the mountains and the seas, a prisoner's life for him there'll be. He knew that it would cost him dear, but yet he dare not say. Where he had been that fateful night, a secret it must stay. He had to fight back tears of rage. His heart beat like a drum. For with the wife of his best friend, he spent his final night of freedom. Over the hills and far away, he swears he will return one day. Far from the mountains and the seas, back in her arms again he'll be. Over the hills and far away. Over the hills and, over the hills and, over the hills and far away. Each night within his prison cell, he looks out through the bars. He reads the letters that she wrote. One day he'll know the taste of freedom. Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be. Over the hills and far away, he swears he will return one day. Far from the mountains and the seas, back in her arms again he'll be. Over the hills and far away, she prays he will return one day. As sure as the rivers reach the sea, back in her arms is where he'll be. Over the hills, over the hills and far away. Over the hills, over the hills and far away
重发【过节了,送给大家三首曲子,我亲手弹的哟】 给跪了...重发...刚刚那个发出来居然全是图片...晕死~~ 上次放出过两个demo版的,这次是完整演奏的,答应过在五一期间放出来的~~今天上午去录音室和两个哥们一起录的~~和以前分工一样,我负责用键盘和钢琴制作了背景效果,以及演奏钢琴、铃声等部分效果;Spirit Luo依然是吉他手与贝斯手;某渣渣同学负责了鼓点...当然后期制作混音什么的也是我做的...两首曲子,希望大家喜欢~~节日快乐~~ Keyboard&background:CloudK Guitar&Bass:Spirit Luo Drum hit:某渣渣 The Crow, The Owl And The Dove (Instrumetal Played by us) The Crow, The Owl And The Dove Don’t give me love, don’t give me faith Wisdom nor pride, give innocence instead Don’t give me love, I’ve had my share Beauty nor rest, give me truth instead A crow flew to me, kept its distance Such a proud creationI saw its soul, envied its pride But needed nothing it had An owl came to me, old and wise Pierced right through my youth I learned its ways, envied its sense But needed nothing it had Don’t give me love, don’t give me faith Wisdom nor pride, give innocence instead It rested on my armI touched its calm, envied its love But needed nothing it had Don’t give me love, I’ve had my share Beauty nor rest, give me truth instead A dove came to me, had no fear A swan of white, she came to me The lake mirrored her beauty sweet I kissed her neck, adored her grace But needed nothing she could give Got to grieve her, got to wreck it Got to grieve her, got to wreck it Got to grieve her, got to wreck it Don’t give me love, don’t give me faith Wisdom nor pride, give innocence instead Don’t give me love, I’ve had my share Beauty nor rest, give me truth instead Last ride of the day(Instrumental Played by us) Last Ride of the Day We live in every moment but this one Why don't we recognise the faces loving us so What's God if not the spark that started life Smile of a stranger Sweet music, starry skies Wonder, mystery, wherever my road goes Early wake-ups in a moving home scent of fresh-mown grass in the morning sun Open theme park gates waiting for Riding the day, every day into sunset Finding the way back home Once upon a night we'll wake to the carnival of life the beauty of this ride ahead such an incredible high It's hard to light a candle, easy to curse the dark instead This moment the dawn of humanity The last ride of the day Wake up, dead boy Enter adventureland Tricksters, magicians will show you all that's real Careless jugglers, snakecharmersby your trail Magic of a moment Abracadabra 结束曲 第三首曲子 Imaginaerum 最后祝大家节日快乐~~
【重发】【Played by us】三首曲子祝大家节日快乐 给跪了...重发... 上次放出过两个demo版的,这次是完整演奏的,答应过在五一期间放出来的~~今天上午去录音室和两个哥们一起录的~~和以前分工一样,我负责用键盘和钢琴制作了背景效果,以及演奏钢琴、铃声等部分效果;Spirit Luo依然是吉他手与贝斯手;某渣渣同学负责了鼓点...当然后期制作混音什么的也是我做的...两首曲子,希望大家喜欢~~节日快乐~~ Keyboard&background:CloudK Guitar&Bass:Spirit Luo Drum hit:某渣渣 The Crow, The Owl And The Dove (Instrumetal Played by us) The Crow, The Owl And The Dove Don’t give me love, don’t give me faith Wisdom nor pride, give innocence instead Don’t give me love, I’ve had my share Beauty nor rest, give me truth instead A crow flew to me, kept its distance Such a proud creationI saw its soul, envied its pride But needed nothing it had An owl came to me, old and wise Pierced right through my youth I learned its ways, envied its sense But needed nothing it had Don’t give me love, don’t give me faith Wisdom nor pride, give innocence instead It rested on my armI touched its calm, envied its love But needed nothing it had Don’t give me love, I’ve had my share Beauty nor rest, give me truth instead A dove came to me, had no fear A swan of white, she came to me The lake mirrored her beauty sweet I kissed her neck, adored her grace But needed nothing she could give Got to grieve her, got to wreck it Got to grieve her, got to wreck it Got to grieve her, got to wreck it Don’t give me love, don’t give me faith Wisdom nor pride, give innocence instead Don’t give me love, I’ve had my share Beauty nor rest, give me truth instead Last ride of the day(Instrumental Played by us) Last Ride of the Day We live in every moment but this one Why don't we recognise the faces loving us so What's God if not the spark that started life Smile of a stranger Sweet music, starry skies Wonder, mystery, wherever my road goes Early wake-ups in a moving home scent of fresh-mown grass in the morning sun Open theme park gates waiting for Riding the day, every day into sunset Finding the way back home Once upon a night we'll wake to the carnival of life the beauty of this ride ahead such an incredible high It's hard to light a candle, easy to curse the dark instead This moment the dawn of humanity The last ride of the day Wake up, dead boy Enter adventureland Tricksters, magicians will show you all that's real Careless jugglers, snakecharmersby your trail Magic of a moment Abracadabra 结束曲 第三首曲子 Imaginaerum 最后祝大家节日快乐~~
【过节了,给大家三首曲子,我亲手演奏的哟~~】 上次放出过两个demo版的,这次是完整演奏的,答应过在五一期间放出来的~~今天上午去录音室和两个哥们一起录的~~和以前分工一样,我负责用键盘和钢琴制作了背景效果,以及演奏钢琴、铃声等部分效果;Spirit Luo依然是吉他手与贝斯手;某渣渣同学负责了鼓点...当然后期制作混音什么的也是我做的...两首曲子,希望大家喜欢~~节日快乐~~ Keyboard&background:CloudK Guitar&Bass:Spirit Luo Drum hit:某渣渣 The Crow, The Owl And The Dove (Instrumetal Played by us)The Crow, The Owl And The Dove Don’t give me love, don’t give me faith Wisdom nor pride, give innocence instead Don’t give me love, I’ve had my share Beauty nor rest, give me truth instead A crow flew to me, kept its distance Such a proud creationI saw its soul, envied its pride But needed nothing it had An owl came to me, old and wise Pierced right through my youth I learned its ways, envied its sense But needed nothing it had Don’t give me love, don’t give me faith Wisdom nor pride, give innocence instead It rested on my armI touched its calm, envied its love But needed nothing it had Don’t give me love, I’ve had my share Beauty nor rest, give me truth instead A dove came to me, had no fear A swan of white, she came to me The lake mirrored her beauty sweet I kissed her neck, adored her grace But needed nothing she could give Got to grieve her, got to wreck it Got to grieve her, got to wreck it Got to grieve her, got to wreck it Don’t give me love, don’t give me faith Wisdom nor pride, give innocence instead Don’t give me love, I’ve had my share Beauty nor rest, give me truth instead Last ride of the day(Instrumental Played by us)Last Ride of the Day We live in every moment but this one Why don't we recognise the faces loving us so What's God if not the spark that started life Smile of a stranger Sweet music, starry skies Wonder, mystery, wherever my road goes Early wake-ups in a moving home scent of fresh-mown grass in the morning sun Open theme park gates waiting for Riding the day, every day into sunset Finding the way back home Once upon a night we'll wake to the carnival of life the beauty of this ride ahead such an incredible high It's hard to light a candle, easy to curse the dark instead This moment the dawn of humanity The last ride of the day Wake up, dead boy Enter adventureland Tricksters, magicians will show you all that's real Careless jugglers, snakecharmersby your trail Magic of a moment Abracadabra
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