Quantum Gravity 3

Any meaningful theory of quantum gravity that makes sense and is predictive at all energy scales must have some deep principle that reduces the infinitely many unknown parameters to a finite number that can then be measured.

* One possibility is that normal perturbation theory is not a reliable guide to the renormalizability of the theory, and that there really is a UV fixed point for gravity. Since this is a question of non-perturbative quantum field theory, it is difficult to find a reliable answer, but some people still pursue this option.

* Another possibility is that there are new symmetry principles that constrain the parameters and reduce them to a finite set. This is the route taken by string theory, where all of the excitations of the string essentially manifest themselves as new symmetries.

— Wikipedia on Quantum gravity

2010.06.04 Friday ACHK

傷逝 5

d_2017_12_31__21_34_58_PM_Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.

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2010.06.04 Friday ACHK

迷宮 4

這段改篇自 2010 年 2 月 7 日的對話。

(LWT:請教人之前,應該要有什麼準備?)

先要清楚自己有什麼問題。

(LWT:如果想不出自己有什麼問題呢? … 有時會知道自己錯,但不知道錯在哪裡,導致不知從何問起。)

不會有「想不出問題」的情況出現的,因為如果真的想不出問題的話,「想不出問題」本身,就是一個問題。那樣,我就可以教你一些方法,有系統、有效率地找出自己有什麼問題。今天我教你的「精讀筆記/Tip Paper」方法,正正是有這個作用:找出自己因為有什麼問題,不知道什麼東西,而導致不懂做題目。 

如果有某一課,你歸納「精讀筆記」時,歸來歸去都歸不到的話,你可以請教我。例如,這一課背後的重點是哪幾句,你未必可以輕易知道。要知的話,要有很多經驗才可以。或者說,要知的話,要比現在的課文內容,高一個層次才可以。情形就好像「走迷宮」一樣:你在「走迷宮」時,不會看到迷宮的結構。要看到迷宮結構的話,你可以用直升機。「老師」的角色就好像「直升機」一樣,可以幫你看到迷宮的平面圖,令你即時看到每課背後的精髓。

只要你維持「歸納『精讀筆記』」的習慣,有很多地方,你自然知道如何問。

— Me@2010.06.03

2010.06.04 Friday (c) All rights reserved by ACHK