g****t
发帖数: 31659 | 1 那天听你说,物理系100个人只有不到一个看过Dirac 约束哈密顿.
然后我google了下,发现一个和约束哈密顿很有关的
loop quantum gravity(LQG),号称是和String theory并列的
一个approach.这个LQG现在流行吗? |
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C********n
发帖数: 6682 | 2 约束哈密顿之所以重要是因为物理里最重要的一个场方程就是规范场，规范场决定了
所有的相互作用,包括引力也是一种规范场，但是规范场是有约束的，这个约束导致
了正则量子化用在规范场上是非常困难的，我猜这可能是为什么dirac对约束量子化
非常感兴趣的原因
电磁场本身还好，但是non-abelian的规范场量子化这个问题一直到60年代末(?)才被
t'Hooft解决，他用的是路径积分的办法，路径积分的一个很大问题就是路径积分本身
在数学上不是well define的,所以一直到90年代还有人在研究用别的办法量子化
一般的规范场
LQG 以前挺火的，90年代以后渐渐让位给了string
卢昌海的主页貌似介绍过一些LQG的知识，你可以去看看
http://www.changhai.org/articles/science/physics/quantum_gravity1.php |
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g****t
发帖数: 31659 | 3 前面我查到,RIM 的老板给LQG一个先驱了一亿美元,
估计LQG还能活一段. |
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g****t
发帖数: 31659 | 4 黑洞熵是在LQG,String之前的,然后LQG,String都要match这个吧? |
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h********0
发帖数: 12056 | 5 people working in lqg are typically classified as
a bunch of crackpots, I think this is a bit too harsh.
But if you take a look at the article published in sci American (?)
where Witten's name is listed together with a few
obscure lqg names (fotini, lizi) as some most influential
theoretical physicists, then you know why these
people deserve the treatment. |
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m**********e
发帖数: 12525 | 6 这些理论candidate的本质是引入更多的可调参数
可调参数一多,你就可以凑出任何你想要的结果了.
supersummetry是这样--多了一整套super partner,你想咋调就咋调
string也是这么回事情,本来点粒子你变成弦,一下多了无数个参数,
妈的,什么问题都可以给你解决
丫说的LQG也是这么回事 |
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x****6
发帖数: 4339 | 7 "op quantum gravity (LQG) is a theory of quantum gravity, merging quantum
mechanics and general relativity, making it a possible candidate for a
theory of everything"
这玩意跟痫论一样，都抢 theory of everything的交椅。 |
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g****t
发帖数: 31659 | 8 那LQG,String都死了.
引力量子化怎么办?
不玩了? |
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g****t
发帖数: 31659 | 9 那个拿到钱的哥们新写了文比较LQG和String,很幸福的样子. |
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g****t
发帖数: 31659 | 10 LQG那个黑洞熵是因为差个常数?展开科普下?
Dirc那个约束哈密顿的方法我记得有不少人举过反例.从数学方面物理方面都有.
所以后来应该是在量子场论里面非主流了.这点我觉得他说的是对的.
这个你正好说反了，Loop到现在还没把黑洞熵掰扯清楚。在90年代中期，Loop的人才还
不少，正因为黑洞熵这个危机，大部分人都撤退了，才成了现在这个局面。
另外，你说100个物理系的不到一个看过dirac的那本哈密顿约束量子化的书？怎么可能
？即使要把规范系统的量子化、brst量子化搞清楚也得从约束系统开始看吧，应该很多
人都看过了。除了狄
拉克那本小薄书，老温的书里也讲了约束系统，我还看过一本quantization of gauge
systems，里面也花了很大篇
幅讲。 |
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c****e
发帖数: 2097 | 11 i don't happen to think that all the work starting with Bryce Dewitt and
Abhay Ashtekar are nonsenses. well, Lee Smolin et.al. tried to develop
it a bit, but not successfully. one of the problems was pointed out by
Ed Witten, which was that the Kodama state Lee proposed as the va-
cuum state was not a physical state. It had a very specific pathology,
argued Witten. But witten's argument was not really rigorous, more
heuristic. So wondering if any LQG guy is around to talk in some depth
about tha |
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w****1
发帖数: 4931 | 12 Ok I don't know these two guys. I talked to a couple some sort of "experts"
in LQG before, and I wasn't impressed.:) About Lee Smolin, I totally agree
with Lubos: his papers are child's play. |
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c****e
发帖数: 2097 | 13 You don't know Bryce DeWitt? Did you not read the very first serious
papers on canonical quantization of gravity? I thought those were
the 3 papers by DeWitt :D I guess you meant not to put those 2
brighter guys with Lee Smolin.
Lubos is probably right on many things, but apparently there's 1 LQG
speaker in strings this year. I just like to use my own judgement
instead of others, however it's hard to have time to go into that
literature, as it's pretty unenlightened.
I don't want to overstate it |
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c****e
发帖数: 2097 | 14 ok, let me take some words back, i meant by models the ones particle
physicists like to construct these days and all look identical sort of.
personally i think work such those done by Landau are really deep.
and yeah, without some miracles, generic knowledge is equally
unpredictive. so, i still maintain that i do think discussing
QG is deeper than a lot of effective field theory discussions.
i still wanna understand some of LQG. |
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h********0
发帖数: 12056 | 16 LQG is so boring! If you want to do fundamental physics,
go for string. |
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c****e
发帖数: 2097 | 17 all consistent quantatitive theories have quantatitive predictions. even
inconsistent ones have outputs. wwhich however cannot be called predictions.
this includes for example much current work on lqg. esp. work by the
famously incompetent lee smolin.
note toobthat stupidity on part of present theorists also does not mean a
theory cannot predict sharp results for all phenomena in its purpoted realm
of validity. for example we do not know the existence of stable solutions of
the navier stokes equ... 阅读全帖 |
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r******y
发帖数: 3838 | 18 ideas of LQG are more interesting。 |
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