武夷山分享 http://blog.sciencenet.cn/u/Wuyishan 中国科学技术发展战略研究院研究员;南京大学信息管理系博导

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A Brief History of Time阅读笔记

已有 4818 次阅读 2014-6-6 06:45 |个人分类:阅读笔记|系统分类:人文社科

A Brief History of Time阅读笔记

武夷山

 

198855日开始读霍金的A Brief History of Time原著(Bantam Books19884月出版),现将阅读笔记与大家分享。由于是给自己看的,翻译得不一定合适。

 

第一章 我们的宇宙图景

P12

追寻完整的统一理论,就会存在一个悖论。科学理论的概念假定,我们是有理性的存在物,能自由观察宇宙,并从而做出逻辑推论。但是,假如真的存在完整的统一理论,它大概会决定我们的行动。于是,理论自身决定着我们对理论之追寻的结果!

 

第二章 空间与时间

牛顿认定的是绝对时间,相对论认定的是光速,绝对时间没有了。牛顿的相对运动抛弃了绝对位置。

 

第三章 膨胀宇宙

将彭罗斯理论中的时间反过来,那么宇宙必诞生于奇点。

 

第四章 不确定性原理

引力场通常很弱,但在大爆炸和黑洞这两种情境下,引力场很强。于是,不能不考虑不确定性原理。

 

第五章 基本粒子和自然界诸力

C对称:对于正粒子和反粒子,自然律是一样的;

P对称:对于任何位置及其镜像,自然律是一样的;

T对称:在时间的正反方向上,自然律是一样的。

 

第六章 黑洞

彭罗斯提出宇宙审查假说:上帝厌恶裸奇点。

霍金曾与加州理工学院的Kip Thorne打赌,若黑洞不存在,Kip Thorne为霍金订4年的Private Eye杂志(博主:英国著名时政杂志);若黑洞存在,霍金为Kip Thorne1年的《藏春阁》杂志。

 

第七章 黑洞没那么黑

黑洞面积不减小,这一行为与熵很像。

 

第八章 宇宙的起源和归宿

霍金是在伽利略去世那天的整整300年后出生的。教皇为伽利略平反的那场“论证会”,霍金也出席了。

(博主:质能可以互换,但是,单纯的热(能)能产生出物质吗?比如宇宙诞生之初的情形,那时是zero size.

弱人择原理说,在时空无限的宇宙中,满足智慧生命发育的条件是时空有限的。好比住在富人区的富人是看不到贫困的。

例如:为什么大爆炸发生在一百亿年前?因为智慧生命的进化需要这么久。

 

第九章 时间箭头

心理时间箭头与热力学箭头等价,总指向同一方向。宇宙无边界论预言了热力学箭头的存在,因为宇宙必须从光滑、有序的状态开始。我们之所以观察到热力学箭头与宇宙论箭头一致,是因为智慧生物只能存在于宇宙膨胀阶段。

 

第十章 物理学的统一

(霍金似乎信心满满)

 

第十一章 结论

大部分科学家忙于描述宇宙是什么,没时间追问为什么。专门追问为什么的哲学家又赶不上科学理论的发展。

到完整理论发现得以普及后,人们就可以讨论“人类和宇宙为什么存在”的问题了。如果我们找到了该问题的答案,那便是人类理性的最终胜利,因为那时我们就明白上帝的心思了。

 

 

 




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"...the dreams of a visionary mind to be closer to reality than the common sense judgment of  the realists." 锛� Car-Gustaf Arvid Rossby
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[2] Kaifeng Bi, Lingxi Xie, Hengheng Zhang, Xin Chen, Xiaotao Gu & Qi Tian. Accurate medium-range global weather forecasting with 3D neural networks [J]. Nature, 2023-07-05
doi:  10.1038/s41586-023-06185-3
https://www.nature.com/articles/s41586-023-06185-3

[3] Kaifeng Bi, Lingxi Xie, Hengheng Zhang, Xin Chen, Xiaotao Gu, Qi Tian. Pangu-Weather: A 3D High-Resolution Model for Fast and Accurate Global Weather Forecast. 2022-11-03
doi:  10.48550/arXiv.2211.02556
https://arxiv.org/abs/2211.02556

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Home
Verification of the high-resolution (HRES) forecast of surface parameters
Overview

https://charts.ecmwf.int/products/plwww_m_hr_wp_ts/overview/parameter?parameter=2m%20temperature

https://charts.ecmwf.int/products/plwww_m_hr_wp_ts?parameter=10m%20wind%20speed&player_dimension=parameter

10m wind speed

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Charts catalogue

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IP: 202.113.11.*   鍥炲 | 璧� 璧� +1 [6]鏉ㄦ鐡�   2022-7-18 22:05
ECMWF
  
European Centre for Medium-Range Weather Forecast
  
娆ф床涓湡澶╂皵棰勬姤涓績
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Verification of the high-resolution forecast of surface parameters
Verification of high-resolution forecasts
  
https://apps.ecmwf.int/webapps/opencharts/products/plwww_m_hr_wp_ts?parameter=10m%20wind%20direction


10 m wind direction
IP: 202.113.11.*   鍥炲 | 璧� 璧� +1 [4]鏉ㄦ鐡�   2021-7-29 17:38
Verification of the high-resolution forecast of surface parameters

Verification of the high-resolution forecast of surface parameters
Verification of high-resolution forecasts
  
Verification of the high-resolution forecast of surface parameters against SYNOP observations.
© European Centre for Medium-Range Weather Forecasts

https://apps.ecmwf.int/webapps/opencharts/products/plwww_m_hr_wp_ts?parameter=10m%20wind%20speed
IP: 220.160.125.*   鍥炲 | 璧� 璧� +1 [3]寮犲繂鏂�   2018-7-24 10:49
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IP: 202.113.11.*   鍥炲 | 璧� 璧� +1 [2]鏉ㄦ鐡�   2018-7-23 23:57
Next, both models differ in availability.  GFS runs 4 times a day, ECMWF runs twice a day.  This means GFS has the opportunity to recover from bad forecasts (say, due to bad input data) by producing more per day.  ECMWF generally outperforms GFS, but if one of the forecast runs was bad, you've got to wait longer for new data.  The reason for the difference in availability is due to the time it takes to compute the model.  Nonhydrostatic models are more computationally expensive, which is why ECMWF is the only global nonhydrostatic model used for operation meteorology.

GFS is free, ECMWF is not. You can get the latest GFS runs for free from NCEP (http://www.ncep.noaa.gov/).  You can even download the model and run it on your home super computer if you are so inclined (http://www.nco.ncep.noaa.gov/pmb...).  To get ECMWF data, you typically need to be affiliated with some organization that pays for it.

Both models produce different products. You will probably be able to get the typic...
IP: 202.113.11.*   鍥炲 | 璧� 璧� +1 [1]鏉ㄦ鐡�   2018-7-23 23:56
What is the difference between the ECMWF, GFS, and other weather forecasting models?
https://www.quora.com/What-is-the-difference-between-the-ECMWF-GFS-and-other-weather-forecasting-models
   
here's a lot of differences between numerical models, so I'll just (briefly) mention the differences between GFS and ECMWF.
  
First both are global models, meaning they produce a forecast for the entire world.  There are also regional models like MM5, NAM, and WRF that produce forecasts specific to a region at a high resolution (I'll talk about resolution later).  Regional models tend to seed their forecasts from global models; GFS provides context for MM5.  I'm not sure what regional models use ECMWF, but I'm sure there are quite a few.
  
GFS and ECMWF use different equations for predicting atmospheric conditions.  GFS is a hydrostatic model and ECMWF is nonhydrostatic.  Hydrostatic models use pressure as vertical coordinates in the forecast (e.g. make forecasts at specific isobars) and ess...

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