# 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

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

（LWT：請教人之前，應該要有什麼準備？）

（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。）

— Me@2010.06.03